I'm not fine with it, like I said, I'm annoyed with Donut.
I get that she was already hurting from seeing what she thought was a kiss, and then discovering in a bad way that Mew was leaving overseas for 2 bloody years. I get that she was overwhelmed and having her BFF confess to her was like a giant shock and thus a sort of tipping point. But it was a shitty thing to do. I'm glad she realized immediately that it was shitty, so something good did come from it, but still, it was shitty to do, and I'm annoyed with her. It doesn't really make me dislike her though, just adds a little more dimension to her character for me. If she hadn't realized she had done something horribly wrong though, that would be an entirely different story.