I have 4 kids and have a 3 bedroom house (we also have a sunroom we turned into a bedroom). The 8mo is a girl and has her own room, the 4 year old twin boys share a room, and the 6 year old boy has his own room (the sunroom).
We have done a lot of room shuffling. But one thing is for sure, the kids have never slept in our room, with the exception of a stormy night or one of them being sick.
Before the baby was born the 6yo had a bedroom, the twins shared a room and the sunroom was the playroom. Then we moved the 6yo to the sunroom, gave one of the twins the other bedroom and everyone had their own space. When the baby came, we moved the twins back in together and gave the baby the other room. The oldest boy felt left out, so we moved him into the twins room and turned the sunroom back into the playroom. They ended up playing all night and the room was tight, so we finally settled on giving the oldest the sunroom, the twins sharing one room and the baby having her own room.
Out of all these situations, the current one is working the best. I did enjoy having one room with all the toys, but with our small house, this just isn't possible. The twins are use to being together and have adjusted to sharing the room. The oldest boy is in school now and enjoys having his own space away from his brothers.
My advice to you is to keep them separate in their own rooms. The longer you let your daughter sleep with you, the harder it will be to get her out later. You said her room is already decorated for her so maybe you can convince her with a new accessory for her room like a tent over her bed.