The powered/nonpowered speaker most likely are not the issue, since both
should work, I have never heard that a sound card only works with powered
speakers.
Many older, cheaper sound cards lacked an amplifier, and would only work
with powered speakers.
The best way to test is use the "line out" from the sound card, (not the
speaker out), buy a new line (stereo to RCA), connect the sound card to her
amplifier/receiver system, that way you can test either music CD or mp3, and
forget about her cheap PC speakers.
