I'm wondering how much stress this is causing you and if its a bit of a vicious cirlce, she cries, you get more stressed, she picks up on it and cries more?
If you think that could be about right,I would make use of as much help as is being offered, use the time to spend with your son and relieve the feeling that he's getting no attention and have some 'me' time, then I think you'll find you and your daughter will both be happier with things.