I don't think she intended to be terrible but since we only saw one side of the story it made it seem that way. I feel like it's possible that she had the same unsure feelings and didn't wanna mess up their friendship but took the last weeks events as confirmation that her love was requited and acted on it.
I get that this is just a story and I agree there's nothing wrong with putting this in a story, but just for the well-being of all y'all, I want you to know that what Dongha was saying about Sanho accepting him is subtle emotional manipulation because you can love someone and not be ready for sex and saying things like that can pressure you and cause trauma so don't let yourself get bamboozled if you're in the same situation
I thought I was the only one seeing this (≧∀≦)