I don't think that Ginny would have a huge problem meeting up with Michael Corner. To sum it up, they basically just... ditched each other, really. Their break up wasn't really traumatizing or violent or anything like that, so there's really no reason as to why Ginny would have a problem with meeting him years down the road.
To me, Ginny doesn't seem like the kind of person who would hold a really big grudge against someone over a small school romance. It really was nothing that extreme, and I think that an older Ginny can see the light and realize that Michael Corner isn't a completely horrible person. I think she would be willing to give him another chance. Maybe she'd hesitate momentarily to consider whether or not it'd be a good idea, because after all, she is meeting up with an old ex-boyfriend, but because it's so long ago and it didn't seem like a very serious relationship, I don't think she would refuse.