Even though I can't stand the company, that Compaq looks pretty solid for the price. It won't be a speed demon, but it shouldn't give her too much trouble.
My current desktop is in my signature. For comparison, my laptop is an Athlon 3200+, 512MB DDR (unknown speed), 100GB 5400 RPM hard drive, ATI X200 Xpress (ugh), Altec Lansing speakers (they sound really good), 15.4" Widescreen monitor, etc. It doesn't scream through anything, and it definately bogs down when I'm trying to multitask, but it gets the job done for me... Hell, I can ever play World of Warcraft perfectly well.
For anything Windows Xp or newer, I would highly suggest 512MB - 1GB of memory minimum. Going with less that will give you some trouble.