If that were true, this thread wouldn't exist. She would have told her ex to take a hike.
Um, no. Had she not reciprocated his interest when he got in touch, you would not be in this situation. This is on her. She was perfectly in control and able to say "no thank" to ex, but she didn't. She is a bit angry at him for messaging? Please. She could have put a stop to everything very easily.
Women with super strong feelings don't consider taking an ex back. They just don't. I know you don't want to hear it, but you need to be real here.