Gosh, that's a tricky one. I can't really help as far as the steps go and how people normally do it. I'm sure lots of people will advise on that. I'd say that if it were me I'd probably send a nice message and include a light version of the purpose, like tell them I had not forgotten them and had always wanted to say "xyz." If you just send a general "hi" message and she doesn't respond it might be harder to follow up with the "real" message. I think it's touching that you remembered this person and want to reach out to them. I hope it is well received however you end up doing it.