I don't know anything about the hardware space, but before trying to do this from scratch, I would suggest trying to get in contact with disabled people and find out what solutions they use.

For instance from a brief search I ran across this old mention on /. of a possibly useful technology for your mouse problem. Even if it is wrong, some of the email addresses of people in that thread may be useful contacts in trying to get in contact with other people with similar situations on their hands.

Sorry that is all I can suggest, and good luck with your daughter.