Has she been to the vet since she started acting up again? Sometimes a hidden illness or injury will cause a cat to start acting out.

Otherwise, it sounds like fear-based aggression - take a look at Section 3 of "Common Aggressive Behavior in Household Cats" in this article.

http://www.animalhumanesociety.org/t...household-cats

Possible that she doesn't like sharing the litter box with the other cats... possibly one wanted to use it the same time she did and the fought over it.

Slow reintroduction, managing them so that they are exposed to one another SLOWLY without inducing anyone to hiss or growl.

It will take time (LOTS OF TIME). The article I linked earlier had instructions.