Is the problem not knowing the facts or is the problem anxiety about it being a timed test? My son knows the facts but gets anxious about the timed part.
Buy her a Didj from Leapfrog. It's a handheld video game system that came out last year for older elementary/jr high age children. You can connect it to your computer then modify the games. Like if you have a math game (my son loves the Spongebob one) you customize it to tell it what you are working on -- like the times 5 tables. Then, all/most of the math problems will be the times 5 tables. Or just a broader "single-digit multiplication". Or whatever. Then when she's playing the games, those are the problems she gets. Since it's fast-paced, it encourages kids to answer quickly.
The games themselves are more like 'real' video games instead of the Leapster ones where the activity is incorporated into the gameplay. With Didj games, you play through part of a level then it switches to asking 3-5 problems and after you get those right it goes back to the video game play. You must answer so many questions correctly to continue and complete the level. It keeps track of correct answers and you can unlock extras like backgrounds, higher levels, secret rooms, etc after so many correct answers.
The games with spelling (my son likes a racing game) are nice, too, because we just give it the week's spelling list and those are the ones they do in the games. The Didj is very good for spelling, fractions, grammar, multiplication/division, etc.