Did the owner of the Rottie offer to pa the vet bills? they should. Idiots. I hate when big dog people let their dogs off leash and think everyone is going to be ok with it.
It's not just "big dog people" who let their dogs off leash. I've seen more small, yippy bratty dogs running around shows/barns off leash being more of a nuisance to people/horses and almost getting stomped.
As someone else mentioned, to prevent her from developing major aggression issues towards big dogs, get her into socialization/training classes, or have friends with big dogs bring their dogs over as many times a week as possible, or go to their house. Always supervise the activity, and nix any aggression. Don't confirm her fear when she acts afraid by picking her up, cuddling, etc...it will only further encourage her to be afraid. Make sure these are dogs you know and trust, and preferably has been around before. You also need to remain calm and relaxed, as she will be feeding off of your energy.
It's so hard to train yourself after an episode like this happens. My GSD was rolled by another dog at the dog park when she was a small puppy, and it scared the crap out of her. She was crying, I picked her up, insert a year's worth of trying to undo it, and now we have a socialized, happy-go-lucky GSD.