Sharing a room

Hello, I'm new here so please bear with me while I get the hang of things. 

I have 2 girls, my first is 7 years old, autism, ADHD, PDA, learning difficulties. My second is 2. We live in a 3 bedroom flat, my 7 year old wants to share a room with her sister. I'm a bit reluctant do this as many people are telling me it will make behavior worse. Has anyone shared a room and it actually helped. 

My 7 year old can be extremely demanding, she has hit me but only ever me no one else, she was started on medication a few months ago now and has only pulled my hair once since starting these, she loves attention, and always wants someone with her. With her sister however they are inseperable, she dotes on her. She makes sure she doesn't hurt herself when they play, she cuddles her, blows kisses and helps as much as possible with her. 

I think everyone else is worried she may accidently hurt her but I can't see this. My main worries are her getting her out of the cot to play. 

Thank you