I could give you the answer, and all you would have to know is the e-mail address, but hey THAT IS HACKING.
Anyway, I understand your concern... And even so getting the password is not going to tell you who she talks to really or even what she has said.
Instead I use a keylogger to log everything typed on my computer, you can download a free one from:
Install > read the notes > use! Remember to use it in hidden mode, and to ensure all shortcuts are removed or your daughter will know.
P/N: The above information is for informational puroses. The information is also breaking peoples right to privacy. So be careful.