Don't try to compete price-wise with Dell deals, you will lose.
My recommendation would be to get one of the boards with integrated Radeon or Geforce graphics - the Biostar Geforce6100 is only around $65 shipped and the IGP should be better than the Intel GMA900, plus the upgrade option for PCIe. The Geforce6100 IGP is also likely better than an FX5200.
Actually, my amended recommendation is to not try too hard because if you build her the machine, you'll forever be responsible for it whether a part dies or she clicks on the email attachment like you told her not to, or she downloads screensavers and such and can't understand why the system is lagging and there are tons of porn popups... so she'll expect you to fix it for free because she bought it from you. There are also people (I know some personally) who can't get away from the idea of "name brands." Then there are people (who I also know some personally) who just looks at the bottom line regardless of performance or quality.
BTW, that price from Dell shipped, is that including sales tax? They seem to charge tax no matter what state you are in.
If you still want to build it for her, "sell" her on quality. Ask her if she wants the mass-market and super cheap Kia of the computer world and liken that to the Dell. For performance sake you should price in 1GB RAM and a larger hard drive and tell her those are better choices (they are). Then ask her to price out the same Dell system but with those upgrades... price should shoot up.