I'm in the same situation as you. I use Macs and my wife is still on PCs.
Without knowing specifics about your wifes pc, It is hard to narrow the problem down. I'd be tempted to post on the pc page as well (In case you havn't already?)
I know you mentioned gaps in the music, but is it skipping or lagging? If skipping, I would think it's to do with the audio side of things. If it's lagging, it could be to do with a memory problem?
Have you 'run diagnostics' (In the help column.)
Hope this helps?
Shinobi