Hey zielak,
Welcome!
Hate to say this but... yeah, you probably should. This depends of course on exactly the types of games y'all play. But if she's already hit the "big time" with a game that's too much for your video card, very likely it will happen again and again.
Right now I'm sitting on two games (Call of Duty and Splinter Cell) because I can't quite pull the trigger on which video card I want! lol I was looking at the following on Ebay...
RADEON 9800 XT 256 MB AGP
nVidia GeForce 6800 GT 256MB AGP 8x, EVGA
One suggestion, (which I'll have to follow myself) is don't buy the most expensive one but don't buy one that's on it's way out either! Don't buy one that will
just barely play the current games. If you do you'll be in the same boat next year! :p
If you buy... let us know what you chose and how you like it!
Lyte
EDIT: It occured to me to ask... can you get into the game to tone down the graphic settings? That might save ya from having to buy if you're current card isn't that old. 
And... but sure you have the most current version of Direct X (9. something) and that the video card you have or buy is Direct X 9 compatible.