On walks my dog is super aggressive to other dogs, but at dog parks she's really nice and doesn't really care. Does any one know why she's like that or ways to help her be nonaggressive everywhere?

I have heard the theory that dogs have a fight or flight instinct and by being on the leash you have eliminated the "flight" option, making them more fear aggressive. How you hold the leash can be making the problem worse. By tugging on a leash or keeping it tight can enforce the feeling of aggressiveness. 

Try leash training in your yard walking in the heel position with a slack leash, as well as sitting. Then when you walk your dog and you see another dog approaching have your dog step aside and sit until the other dog passes. Once you dog is comfortable with other dogs passing you can start to work on walking your dog past other dogs.