Question for mature females (sexually related)?

Me and my gf of two years just had sex for the first time 3 weeks ago. It was her first time. I'm having this feeling that she has a high sexual appetite and from my personal experiencing dealing with women like that...they always cheat. We only did it twice and after the first time I asked how often does she get horny and she said all the time. After we did it the second time she said she had an orgasm(which I don't believe). I'm just asking from a female's perspective is it natural that women get turn on to sex that quickly? Especially from only doing it...twice. It just seems kind of weird because most women I know say they don't enjoy it until after they've done it a number of times.