You should make her bring them home. I don't think her mom likes knowing that all her clothes are at your house and probably feels  petty asking for them back. Slowly pack them up for her each time she goes home. I'm sure her mother would appreciate it. 

Skids live at the divorce house half the time but their rooms are practically empty because they keep all their clothes at BMs house. Home for them is at BMs which we have no problem with. We hope it stays that way.

make a big to do about going through the clothes because of the changing seasons. Everything that came from BMs gets neatly folded, packed and shipped back to her “to be nice”. From then on only the clothes you buy for your house stays there so “bm isn’t missing something”. 

Also, if closet space is an issue, maybe pack all of baby’s outgrown stuff in totes and store elsewhere?

My SSs bring nothing with them, because BM refuses to send anything with them. She claims that DH never sent anything home, but really, things are sent home and then get lost in her trash heap of a house. We used to buy clothes for them and then they would want to take them home. BM also thought it was DH's responsibility to provide everything they would wear at our home and then used to request that things like winter coats or dressy clothing get sent home. I bought the kids shirts once, before DH and I were married, because DH wanted to get pictures with Santa. As soon as BM saw the picture, she put in a request that he send the shirts home with SSs and I said, "no way!" 

Now, they are teens and I've stopped caring if they wear the same clothes the entire time they are with us. They have pajamas at our home and usually a warmer sweatshirt, in case it gets cold. They also have extra underwear and tshirts, but rarely tell us when things don't fit, so who knows what fits them anymore. 

They still bring nothing, even if DH asks them to bring things with them. It's a very weird situation, BM would rather that her kids go without than send them with anything (I also think she's too disorganized to make sure they bring anything with them and they are helpless, even though they are now teens).

The dynamic changed when you had kids and she wants to feel part of things.

We had clothes at our house for SS. He did his own laundry, starting around age 11-12. He didn't have to do it weekly, just whenever it was needed. DH had already been teaching him how to do laundry before we moved in together, so it was no big deal.

I wouldn't have minded doing his with ours except that when asked to put his dirty laundry in the hamper, he'd scoop up everything, clean or dirty, and put it in there.

10 is not too young to learn to do laundry.

DH and BM have 50/50 custody of skids, so they have complete wardrobes at each house. Stuff still goes back and forth, because no one limits (or pays much attention to) what they're wearing when they go between houses. DH and BM aren't high conflict, so it's not a big deal.

In your case, I totally understand the space issue, but not the laundry. Unless your SD is changing clothes multiple times a day, I'd think she wears the same amount of clothing at your house whether it's hanging in her closet or going back and forth in a bag. So what she wears needs to be laundered - unless you're expecting her to take her dirty laundry home for BM to wash, which doesn't seem reasonable.

I think your DH needs to do 2 things - (1) force SD to purge her closet/drawers to an amount appropriate for the time she spends with you, and pack up out of season clothes to either take back to BM or store elsewhere in your home (like underbed boxes or totes in the attic or basement) and (2) learn how to do laundry properly and step up his help in that area.

She just wants to feel that she belongs and that it is her home, too. But she does not need to bring ALL of her clothes to keep there.

Definitely have your husband sort through them with her and take a bunch back to Mom's.

In our house everybody does their own laundry. I started that years ago when DH and the kids would leave stuff in their pockets and it seemed it was always my clothes taking the brunt of the abuse.

When Spawn did live with us she and BD shared a closet and there were times when Spawn had more clothes than BD and would put stuff on BD's side of the closet. When that started to happen I would tell her to go through and start getting rid of stuff that was too small or that she no longer wore.

Buy her a hamper of her own to keep her dirty clothes in and have her wash her own clothes.  I have 3 step daughters and 2 BDs.  I did this and I no longer care what they do with their clothes.  If they want clothes at their moms, they can take them back.  Not my problem, I'm not involved.

Nope. Luckily I came here in the beginning of my step journey and found that clothes were such a huge point of contention. It is in everyone's best interest of peace that you just keep the clothes purchased at your house at your house. No packing bags but the skid can wear what they want. Based on our schedule my SS8 wears his school uniform to BM's during the school rotation and then in the summer time I let him wear play clothes that I won't mind going missing or getting ruined. 

This cuts out having to replace anything of hers that gets ruined or lost, it keeps the things you like home and safe, it gets rid of the need for unannounced drop ins by bm and stepkids if they left something behind and it keeps the kid from stressing out over "living out of a suitcase". 

Whatever she brings from BMs goes back with her to BMs. Whatever you guys buy her, stays at your home. Firmly tell her to set her dirty laundry aside from your baby girl's and make her do her own laundry. She is 10. I started learning to do my own laundry when I was 8 years old. It is not that difficult. If she refuses, let it stink up, it's not your problem to deal with, it's hers. If she continues to bring clothes just stick them in bags and send them right back home with her.