Hi. She could be going through a stage of separation anxiety? I have a fan blowing (not directly onto his bed but just onto a corner in his room) for white noise - it drains out noise from outside, when someone is mowing the lawn or even drowns out when my husband is working with his tools outside. You can try and burn a cd for her with songs you sing and play that in her room, or tell her instead of turning on the light she can play with the cd player, it will keep her busy (if she knows how to use it) and she will hear your voice as you sing to her or read a story.
Just a suggestion. But the fan works wonders. The humming drowns noise, but im not sure if it will drown out baby crying...
I also recently purchased a nightlight Twilight turtle (http://www.cloudb.com/ssandf/turtle.html), it changes colors and projects moons and stars on my son's walls, so he stares at that instead of crying for me to pick him up. It seems to calm him down. Some come with an MP3 Player, so you can even record your voice on that perhaps and show her how to use it.
Its not sound sensitive, but im sure you can find something that turns on with sound that can project soft light for her. She might be scared of the dark too?
Good luck!