I got an iPod Touch 4th Gen from a friend, and she left all of her music on it so I could have a larger music library. The problem is, I don't know if there is a way to sync my library with the iPod without deleting all of the music she left on it. Is there a way to sync music from more than one iTunes account onto one iPod?
No, there is no way to do that. However, on a windows computer you can turn on "view hidden files" and be able to copy all of the music files in the music folder directly from the iPod to your computer. Once you've copied the files you can add them to your music library and re-synchronize the iPod.
No, there isn't. Instead, you might want to try copying the songs from the iPod to your iTunes library using a program like Senuti, and then sync the iPod to the iTunes library. Of course, I would only advocate doing this if you have the rights to the music on the iPod *cough cough *.