I never see benchmarks for WoW, so it never crosses my radar. I guess the new
Wrath of the Lich King can actually tax systems a bit. Not extremely but a bit.
That card would run full resolution max detail. If you wanted to step it up a 4850, GTX 260, 4870 could satisfy your friend. One of the issues with getting cards of this level is they start to require greater power sources (PSU).
The 4830 needs about 80w of power which most PSUs can do no problem.
The other cards
4850 = 100w
GTX 260 = 120w-140w (55nm 65nm respectively)
4870 = 130w
A couple deals going on now within your price range.
MSI Radeon 4870 1GB - $169.99 AR + ship
eVGA GTX 260 $149.99 AR + ship
Would she notice a difference? Yeah sure. Is it worth the extra power and cost for the extra performance? Not sure. I'll let a few others chime in to give their take.