It all started on one very bad day a few months back.

Gilda walked into you, and she said you walked into her. One shove led to another and eventually the two of you were fighting in the courtyard. A few blows were traded, but the fight got cut short when Principal Celestia pulled the two of you apart.

That was just the first of many fights. She goes everywhere you go, always goading you or bragging about her superiority in something. Of course, you were both on the same level, but neither of you would acknowledge it.