As far as sensitivity goes I would have to say it depends on her. After i orgasm i get extremely sensitive and dont want to even be touched near my vagina, and other times I dont want to stop. I would have to say its a personal preference.
I was with a girl and we started from a little touching then moved to fingering, started from one finger then two and she started moaning like insane. Then it stopped she made almost no voices, even when I penetrated her. So I though maybe she just came while I was fingering her and then maybe became less sensitive or something.. really, do women become less sensitive after orgasm?
Some girls take quite a bit longer than other to orgasm. Personally I know a few girls that say it is easier for them to orgasm when they are on top. If a girl does get an orgasm TRUST ME you will definitely know...there is no hiding it. Some girls can achieve an orgasm by fingering but you must pay special attention to massaging it as well, it will make it feel much better!