iPad 2 -- update to IOS 7 or stay on 6?

I bought my girlfriend an iPad 2 right around the time the 3rd gen came out. She has resisted downloading IOS 7 because she heard how terrible it is on iPad, and given her aging hardware, she doesn't want to take a step back in functionality. She uses it everyday, and really could not care less about what the UI looks like or fancy animations -- but shes starting to complain that it's been a bit slow lately, it hangs up on certain tasks, and she occasionally has to reboot it to get it back up and running.

So will IOS 7 be an improvement or a detriment to performance? She just wants it to work, and couldn't give a crap what it looks like.

Thanks, guys!