Her story is actually very interesting. I don't buy that she did it just to be vindictive. If that were the case, she could have done worse.
The fact that she still has rage about the whole thing in chapter 4 tells me she still cares about the MC. You don't have that much rage about a situation if the person that did it doesn't still effect you. I think she's been lying to herself for years and this situation is forcing her to confront that part of herself, especially with the way she's visibly still attracted to him by going for the kiss over a blowjob first.
She's not over him. Not by a long shot, and she handled it supremely stupidly.
What I don't understand yet is why she got him on contract and still sent the merc in. Hedging her bets is my guess, but I don't know that for sure yet.