Is her iPod from a PC and you have a Mac? Or Vice-a-Versa? That would happen by a matter of formatting issues.
1) You can unplug the iPod, no real harm will be done.
2) Plugging an iPod into a computer other than the one that it is registered with with not make it very useful to the new computer (if you want to use the iPod you will have to erase it first).
Finally, what is it you are trying to achieve with the iPod? Transfer music? Cause it's not that easy to do.