Hey mom, don't "suggest" your daughter take a break! YOU are the parent, and you need to set limits because you're daughter doesn't know how to. I have a 13 year old daughter who would spend all her time on the computer if she could. But I am very clear that on school days, all school work comes first . . . and done correctly and thoughtfully. Obviously, her grades will tell whether she's putting the correct effort into her schoolwork. And the computer is turned off no later than 7:30 p.m. And on weekends there are still limits, because I want her outside getting fresh air/exercise, etc.
You should consider just making a limit for all electronics activity. On school days she could be limited to 1 - 1 1/2 hours, and the rest of her time should be spent on schoolwork, reading, etc. It is her choice how to spend that time, whether it be on the DS, the computer, watching TV, etc. On weekends she would get a little more time, but still put some limits to force her into other activities and to socialize with "real" people (something my daughter would rather not do!).