Usually schools will offer extra tutoring (sometimes they want to call it special ed but I think they are just generalizing most of the time). Or, if you have the money, you could find her an outside tutoring center. My son is now in fourth grade and it's like he doesn't even use his brain when it comes to that type of stuff. I know first hand just how frustrating it can be. If I were you, I'd talk to her teacher as soon as you can to get their opinion and see if you can set up a meeting with them, the school councilor, and maybe the principal. Discuss your concerns and see where they stand and what they have witnessed from her thus far. I've had to do it every single year my son has been in school and trust me, your involvement will do wonders. Get on a regular speaking basis with her teacher (my son's teacher emails me daily. Even if it's just a behavioral update with a few words), and see if they can't put in place some sort of plan. If you back up at home, what they do in school and stay in constant contact, you may be able to figure out what's going on and how to help her.
Have you had her evaluated by the school to see if there is some underlying cause to her struggles.