Don't want to drip feed so there might be some pointless info 🙈
Been with my DP for 4 years, he has two DD's age 6 and 7. When I met him I lived on my own in a two bed apartment. My spare room was my make up room, so just had my wardrobe, dressing table in etc..
As the kids have got older they started to stay over once a week and they would have our bed and we would sleep in the living room as we don't live near there school so we did Saturday night - Sunday. We had our DD together 18 months ago and I decorated my spare room for her. Suddenly the kids started staying 3 nights a week so we got them bunk beds which takes up nearly all of the bedroom. This hasn't been a problem until 9 months ago when I moved DDs cot into her their bedroom, however as DSD sleep talks it wakes DD up so when they stay over DD sleeps in a travel cot in my room.
A few weeks ago my niece came to stay with the girls and their wasn't any more beds, so DSD asked if she would sleep in DD's cot. I was a bit meh about it but thought why not. But now she won't sleep in her bed and is always climbing in and out the cot. I've told DP I'm not happy with her sleeping in the cot and thought it was a one off thing and he said it's not hurting anybody so why not.
Now I haven't actually got a reason for her not sleep in their other than it just makes me furious for some reason 
So AIBU? Or should DP tell her to sleep in her own bloody bed?