SD brings up her mom in conversation now and again, however that's understandable as she's 12. DH however knows not to mention that dumbass wench's name in my presence.

In your case however, I would say that if you've said it makes you uncomfortable she should cut that crap out and respect your wishes. So I would firmly remind her of this next time it happens.

What does she actually say about her BM in conversation? Does she reminisce or what?

My SD33 sometimes talks about her mother but it's never anything good! I seriously couldn't care less and am mostly amused, as her life is a train wreck.

The fact that it's been brought to her attention that it makes you uncomfortable and she doesn't seem to care, is just rude.

You have said it bothers you. SD says "It doesn't bother ME!" So she keeps doing it. To you. The fact that it bothers you and you asked her to stop should be enough if she's not a total a-hole. Maybe you like being tickled and SD doesn't. You start tickling her. She says please stop, she doesn't like it, but you say "I don't mind being tickled so i'm just going to keep tickling you, mkay?" That would be crazy, right? 

IMHO talking about an X is not out of line.  We talk about the SpermIdiot far more frequently than we do my XW, though my XW does come up upon the rare occassion.

It is not anyhing remotely regularly but ... it does happen.  The SpermIdiot and the SpermClan come up because we have a son that has half of their shallow and polluted gene pool and due to the occassional resurfacing of a SpermClan topic.  A couple of times a year their ever growing balance on unpaid medical costs for SS-31 going back to his birth is invoiced. The CO ordered that any medical costs not covered by insurance were to be split 50/50 between DW and the SpermIdiot. They never paid a Cent. So, twice a year my CPA bride goes IRS on their idiot asses invoicing them for the ever increasing principal, penalties, and interest for half of every Cent that we paid for SS health care that was not covered by medical insurance. Yes, going back to his birth.

She has a spreadsheet with daily compounded interest formulas and IRS penalty matrix formulas in it. She hits  update twice a year, prints out two copies, adds an invoice cover sheet to each copy, and sends one to the Spermidiot and one to SpermGrandHag delivery confirmation.  The delivery confirmation receipt goes in our file cabinet.  Just in case we do decide to take them to court over the unpaid COd expenses they are liable for.

They will never pay. Which is irrelevant to us. We never needed the money.  We just make sure to send them the reminder of how big a collective POS they all are.  Every once in a while SpermGrandHag will call and pout about letting it go.  Nope, you bred that POS, you funded his brood of 4 OOWL spawn by three different baby mamas, you paid his CS obligation and visitation travel, you get a copy of the bill.... twice a year.

My XW, pretty much only comes up when something on STalk triggers a resurfacing of my first marriage and DW and I talk about it.

My skids, especially SD, have always talked about their mother when around us, although they know our relationship with the crazed clown has been ugly. SD has compulsively brought up her mother around us, as if it is a duty. "Mom looks young for her age" (uh, no she doesn't, sweetie); "This crazy street lady called Mom a whore!" (damn...how did she know?). But it's usually, "Mom said this..." "Mom did this...." (we don't care!). The one that did bother me, though, was when SS, in his mid 30s, sat here in our home last year talking about the expensive gifts he had bought his mother when that little pr*** was telling us how "broke" he was and has NEVER given us gifts. But, in our case, they primarily drone on about Mommy for a reaction, I believe. Which is why I've never given them one. I have acted totally normal and even engage in the conversation. 
BUT one trick I've learned when someone is saying something I don't like or that is rude is to turn it back on them, so, in your case: "SD, I'm curious: Why do you talk about your mom so much when you're with us? Do you feel obligated to do that? Why?" 

Though not actually deceased, the SpermClan are all dead to SS.  I make sure to ask when we are on our periodic calls if he has any updates from  his sister or brothers, or anyone else for that matter. The answer is invariably no. He does not talk to them.  They don't call him, he does not call them.

We generally do not discuss them either. Unless, it is an anniversary of some event or DW or me have had a conversation that triggers a thought on them.  Recently one of DW's coworkers was talking about some toxic X/Skid thing.  That triggered DW sharing with that coworker and us doing a catch up on our day discussion that covered it that evening.

Other than that, they are pretty much dead to this side of the blended family equation.

So she lacks social skills? Then stop pussyfooting around her seeing as she won't get it. Next time she starts on about her mother, laugh uproariously and ask her why she thinks you'd be interested in what "that woman " does (try not to call her "that old bat" but if you can't... ).

Be direct, because the 32 year old isnt that bright.

Learn to be unaffected by anything said- I've got one SKID and his monster of a partner say things to get a rise out of me - I literally don't listen. They said something recently that should have cut me to the core but I nodded, heard it but really didn't let it enter beyond. They kept looking at me like "what? is something wrong with her? Why isn't she crying?" What I wanted to say is literally NOTHING you say holds water with me and I have gotten to a place where you could tell me anything and I would not have a reaction. I don't care. Their opinions and thoughts have no weight, quite literally in my mind. Over the last two years I think they are starting to realize I literally don't care and the stupid talk has stopped and now they just make faces at me. My reaction to the "faces" as adults is to just simply do my duty/obligation when I have to see them and then I walk out- I don't even say goodbye. LOL 

or not. If she is that dense where she cannot understand clear and direct language, she might have something else going on mentally/cognitively.

The awful spawn DaughterWife of the person I was with, would bring up her mother when we could meet up for a meal, 'Mom said she wants her bed back' or Mom this, mom that, etc...announcing such 'news.'

They didn't know that I knew that he was still in communication with their mother every day. He offered his ipad for me to use one day, I opened it up to find their (his and ex-wife) string of text messages and emails, all after he denied it. The narcissism with him and those girls were nauseating. Of course he spoke with DaughterWife several times a day. Point being, ex's name or reqeust of return of her bed was intentional during that meal. It was deliberate. This is just one of many times the manipulative little b*tches thought they could play me.

The last few times they did this, I jumped in the conversation and lit it up...'so what is your mom and her husband up to nowadays?' 'Did she ever gain a second digit on her IQ?' 'Wow, she must be so proud of you failing last semester! What words of encouragement did she give you to pass next semester? Oh right, she never went to college, remind me, did she even graduate high school?' DaughterWife pis*ed away his money for college/housing/lifestyle, time and time again, and would brag about making such high grades (in one elective class), leaving out the other 3 classes she was failing.' Fake, fake, fake. 

Yes, I was petty and passive aggresive, on purpose. Just the look on their faces was satisfying to me, lol! I knew I was leaving so took the opportunity to openly discuss their mom. Of course, he tried to argue with me later but I gave him the Garfield the cat look...uninterested, indifferent, unaffected, no response. 

So jump in and make the convo about the mom/ex or choose not to listen to it, she is likely trying to get a rise out of you or make you feel like you're not there. Either way, it's just rude.