Being capable of understanding emotions of another person and feeling for them is basic empathy and something which sets apart regular people from psychopaths. Am not sure if it's really in favor of Cherry to put her on the shelf with the latter. And it's really not "nothing", Cherry had active role in hurting Lena. She knew exactly what she was doing, she knew how Lena was going to feel when that affair comes out but did it regardless. It's the same selfishness we see in Gillian.It is major deal if we take the act separately. Lying to someone, fucking someone's boyfriend. But it's just general not very moral behavior. Bad, but understandable. And why would she feel something for the emotional well being of her adversary of all people? Compared to the things Gillian and Axel had done it's... nothing.
Am not saying it's not understandable. But it's simply behavior of a shit human being, and that's what Cherry ultimately is. She doesn't need nor deserves to be excused for her actions.
Leaving aside people in love are ready to do a lot of objectively stupid things which to them make perfect sense, she didn't need to do the reveal in person. Tipping Lena off anonymously would work just as well.It doesn't work that way. Revealing that you are fucking someone's boyfriend would just piss said boyfriend off, cause he will lose another willing pussy or, maybe, more than that. I could understand if she would be stupid enough to think like that, but she wasn't and said nothing.