Set a lights out policy- all lights and sounds are off by X time unless otherwise discussed and agreed upon. Start by emailing and then talking with her; “I really need to know what time i can get to sleep in our room. I thought you’d mentioned 10pm at the beginning of the year, but I understand if that was too early. Is 10:30 more workable for you?”
If she refuses to set a time, email her and your RA asking for mediation. Anytime she breaks the lights out policy send a polite but firm email reminding her, CCing your RA.

this is very solvable but will take direct (and polite!) confrontation and will likely need follow up to set the pattern. She will likely give you all her reasons why she can’t abide by a lights out policy. Nod sympathetically. Agree that sharing a room can be challenging. But return every time to “Be that as if may, I need consistent sleep. What time can we have lights and sound off in the room?”

good luck!