Instead of telling him what he is doing wrong (which he will not listen to) tell him that it really doesn't concern you and that you do not want to hear about it. And then make sure that his financial follies do not impact you.

"my DH is a 24 hour bank"

This is the only part that would bother and perhaps affect me. Is he using joint funds to bail his daughter out of all her financial messes? I'm guessing if the SD is 30 that Dad is somewhere in his fifties? Does Dad plan to always be around to bail out his daughter or that he won't need his own money for retirement?

You mention in your profile that your DH's first wife passed from cancer. So I don't want to just assume everything and anything he is giving to his grown daughter is out of joint marriage funds. He, for example, may be handing out money that once belonged and was earned by his first wife and he feels this cash isn't part of the new marriage package? Maybe legally his, but not in his opinion to necessarily benefit his new marriage.

Anyway... unless the assistance being given is somehow directly affecting you and your joint accounts, I'm not sure I'd want to hear all about the SD's dysfunction. Who cares if she is a hypochondriac. Why read her social media crap. The woman lives far away from you and doesn't have to have any daily impact on your current marriage at all. You don't have to see, talk to or have anything to do with her.

And again, unless it is somehow your cash going to the SD or your joint finance accounts that is directly taking cash from your shared expenses and needs, it's probably best DH doesn't tell you every last little detail of the SD. As you say, it only stresses you out.

Maxing out credit cards, falsely claiming to be ill at all times and being an ungrateful person , while not merit earning qualities to have, I'm not sure if it's worth stressing over and potentially harming your own health and marital relationship.

I think you'd have to give more details on how her behavior directly affects you. But for sure, you are not alone in your feelings about disliking the behavior of a full grown stepchild. Nor or you alone in having a stepchild who terribly uses and shows no appreciation towards their parent.

Lots of members here who can relate to stepkids who treat their parent poorly, demands Daddy fix things and uses their father shamelessly. You're also not alone in having a DH who tries to hide it all from their wife.

Keep reading the different postings here under adult stepkids and you'll quickly see you are not alone nor are your issues a single case. I, myself, have a SS older than your SD who thought his father and I should co-sign for a house for him AND give him cash upfront for a down payment. Yeah, didn't happen. But my DH never attempted to take the request seriously nor asked me if we'd consider it, no, SS got an immediate 'h*ll no, straight up and out of his father.