this is what I think, if a girl has had sex enough so that she cant remember how many times (more than 40 times) and she has never, or she has only cum a few times then it could be a number of things:

1.she hasent yet discovered what really gets her off.
2.she's never really let go of her inhibitions during intercourse.
3.she has a physical problem and should see a doctor.

90% of the time I'd say it's likely to be one of the first two.