You can gauge her libido early on...when my GF and I were dating she would initialize sex as often, if not more often, than I did. That was a major factor in wanting something more than causal with her. Even after 8 months our frequency is only increasing / getting better! We actually snuck away during her friends bday party for a quickie (at her request) last month. There are times when I actually have to say no to sex (I'll still go down on her, it's common courtesy) usually because I'm too sore. In the words of Zapp Branagin "the spirit is willing, but the flesh is spongy and bruised."

I found with the other girls I've dated that after 6 months it's like pulling teeth to even get a BJ, let alone have sex. Always the same excuse (I'm too sore from last week still, I'm just not in the mood, I have a headache, my roommate is home, I'm too tired maybe in the morning (spoiler: she's still too tired in the morning) and even if you do get some, they want to have 1 go and then that's it. No round 2, no round 3.)

Sooo I guess for me I won't even consider taking the relationship to the next level if she doesn't have a high libido. GF and I discussed it and our ideal amount of sex is the same (at least once a day, or 2-4 times in one go with a day of rest after). My ex had a average / low libido and there were so many arguments from it. Sex should be a strength in your relationship, not a source for constant arguments and hurt feelings.