H.,
Do you plan to have the new baby in your room to start? Maybe you can put the transition off a bit longer, until your new baby is a few months old. How many more months do you have to go?
I see a huge difference in my son as he approaches age 5. He is constantly surprising me with what he chooses to do on his own, what he is no longer scared of, etc. If you could even wait until spring, the days are longer, it isn't so dark in the morning, maybe that would help with the transition.
I agree with the previous poster to review exit plans, invest in good alarms, and make sure your daughter is able to find her way to the front door if needed.
Another option is to set her room up in the basement. Put all her stuff down there, but make sure there is a place she can sleep (in a sleeping bag maybe) in the old room. My SIL did this when they moved to a new house. Her oldest needed time to make that transition downstairs, so he continued to sleep in the same room as his sister until he was ready. She could play down there, get dressed, etc., but maybe still sleep upstairs until she is really ready to make the big move.
Good luck, and congratulations on your soon to be baby!
J.