Revenge cheating is undignified and counterproductive. However, being cheated on is an extremely painful and upsetting thing to experience. I'm not sure that I would judge someone based on something they did while they were dealing with something so difficult (unless they committed a violent crime, which is ALWAYS a red flag). In addition to that, this was three years ago, and she might have changed in that amount of time.
If she's a wonderful girlfriend to you, cares about you, and treats you with respect, then I don't think I would be too concerned about what she did three years after being cheated on. Unless, again, it was a violent crime or something else very extreme. And revenge cheating, while a bit low, is ultimately not an overly extreme reaction to being cheated on.
I don't understand the description well, it contradicts the title. Is she your ex or your girlfriend? Either way, it does show a bad side of her personality but it really depends on how she is today. She might have changed.
Huge red flag as they come! As someone who has dated women like this, those who have cheated in the past, almost always cheat on you again. They are always "justified" in doing it, its either revenge or "you didn't satisfy them enough." they are rationalizing their behavior. Save yourself a lot of future grief and end it now, before you really fall for her.
It was 3 years ago and before you, why care. I should think she's changed in that amount of time. If not, simple, don't cheat. If she really wanted to get revenge she would've gone for his brother or dad. I can get a new best friend but sooner or later I gotta deal with family.