Let us objectively examine this from a cost-benefit analysis perspective. Unless this girl is some sort of Unicorn, the following is probably true about her.
1) She's probably good at sex, however, she's very likely to be psychologically damaged and unable to form an emotional attachment to men due to the sheer number of sex partners she has likely accumulated. Therefore, a short term, fun relationship with this woman is certainly possible, but your prospects for long term stability are, sadly, minimal.
2) Women generally care more about social acceptance than men do. It is a rare woman that can make an rational, informed decision on whether or not to become a prostitute. Considering that it is distasteful work, highly illegal, and very dangerous, it is very likely that your girlfriend has poor judgement, and terrible impulse control. Only you can decide the answer to this though, i would observe her behaviour more and then make a judgement.
3) People with poor judgement and impulse control are more likely to abuse drugs, which could lead to prostitution in the first place. Now dont get me wrong, i for one, love drugs of all sorts, but for a lot of people this is a deal breaker and there is no way to ask her without hurting her feelings.
4) Prostitutes tend to see sex as transactional. The fact that she waited two months to have it with you, combined with her aforementioned lack of impulse control and poor judgement, makes me think she is not attracted to you physically, otherwise, why would she wait so long. If she really wanted you and was scared that you would move on because you were high value, she would have used her pussy on you sooner, trust me dude.
There is some aspect of the relationship, that you are leaving out, and while she might insist on paying a "Lot" of times, i am willing to bet my bottom dollar you're still shelling out 80% of the money in this relationship on a grad school loan.
This is where it gets complicated and you will have to do some thinking. All of this extra crap is baggage that will come and bite you in the ass later.
Is this girl the sort of exceptional unicorn that you would put up with this extra bullshit in order to keep her around? Or is she just average, and youre just excited to have someone because you don't usually get laid? Judging from your writing, it is probably the latter. Only someone desperate for sex, is willing to wait 2 months, and/or has women make him wait 2 months.
Frankly, for me to consider dating an ex prostitute she would have to also be a gourmet chef, a working professional (doctor, lawyer, accountant, banker), extremely attentive and caring, as well as loyal, and fucks on demand 24/7. This is the only way to offset the glaring personality deficits present in most sex industry workers.
Furthermore, even though i will be downvoted into oblivion on this subreddit, here are some medical articles to corroborate my views.
http://www.sciencedirect.com/science/article/pii/0191886996000530
http://www.sciencedirect.com/science/article/pii/S0306460304003211
http://www.sciencedirect.com/science/article/pii/S0002713809606592
http://www.sciencedirect.com/science/article/pii/S0924933809704791
I could go on and on.