At 3.5 you can be stern with her. What are her current punishments for getting out of bed or screaming? I am a frim believer in consequences for actions. A repeated punishment every time she gets out of bed or screams should help.

Depending on your comfort level have you ever thought of just closing the door and walking away? She will scream that is for sure but if you keep going back to her then it just leads her to believe that her tactics work. My own son would just open the door when I did this so I keep a child saftey doorknob lock thingy in his room and when he is in a "big time out" or if he won't stay in bed I pop it on. Then after the time out or once he's asleep I remove it. You'd have some rough nights and I'm sure your other child wouldn't sleep with the screaming but a few nights of that and it might just work.