The newer cards offer better audio quality, but for most listeners its overkill. Mainly the new cards are for better game support, multichannel speakers, digital output, high quality recording etc.
Unless she is a musician, she probably wouldn't notice any difference with a new card. Of course with audio, what people think they are hearing is often more important that what they actually are hearing.
(Penn & Teller put different labels on NY City tap water with fictitious names and prices. Even though all the water came out of the same dirty hose behind the restaurant, people honestly though they could taste differences between brands and most honestly enjoyed the $10 bottle far more than even enjoyed tap water)
So if sound is really important to her, and she enjoys her music less knowing its form a cheap sound card, then an upgrade would not be a waste of money.
A $35 SB Live 5.1 is the budget choice giving you the most band for your buck, but a $100 M Audio 7.1 Revolution definitely says "I Love You".
BTW All of my friends thought they can tell the difference between CD-Audio and a PROPERLY ripped mp3. But when put to a double blind test none of them could! Even my friend with the $100+ sound card and $400+ speakers failed the test
. (This was with a 128kps mp3 ripped form a CD mastered in the 1980s).
Of course with a digitally mastered CD, quality headphones and practice almost anyone can learn to tell the difference.