Hi D.,
I have a little one who will be 3 in October. She was in a crib in my room until about 3 weeks ago. Well, the crib is still there, but she climbed out of it within seconds, (for about 6 months) so we took the side off so it's like a day bed. She's sneaky; she didnt want anyone to know she could do it, and only did it when nobody was looking.
We also put a single bed in my older daughter's room at the same time.
I have 4 kids and live in a 3 bedroom house. My oldest daughter, 18, just moved to her fathers to go to college, so my 16 year old daughter has a room to herself for the first time, but that lasted only about a month before I put the youngest girl in there.
The boy has a room to himself since he is the only boy, he's 8.
I'm keeping the crib in my room, I sleep in the basement, so when my daugher goes away for weekends or overnight, the "baby" sleeps in my room, in her 'big girl crib'. And when the 16 yo is home, she sleeps in her 'big girl bed'. She stays in both beds with no problems, just the occasional walk back to bed and tuck in when she's not so sleepy. But is well with that and she sleeps all night without problem.
She is upstairs now, in the room by herself, in her bed taking her nap, and I don't have any problems with her getting into stuff that she shouldn't unless my older daughter leaves stuff out.
If your baby is going to be in a room by herself, there wont be so much for her to get into. Maybe keep the toys minimal and clothes put away. Lotions, powders and such- you can only keep them put up high and make sure there is nothing to make climbing to get them easy, or out of the room completely. (my little one loves to climb!)
You shouldn't have a problem. I just got my little one excited about the big bed, she loves it.
good luck.