Hmmm. I'm going to weigh in on the other side here and not crucify someone for past indiscretions. There are a few other points to consider though.
First, I've known women who toss out a red herring to check for reaction. Say she's been with five or even fifty but adds a zero to see whether you flip out. If this is early on in the courtship, then that tells her how you handle potential deal-breakers. This also tells her whether she has to hide things from prospective mates, and also what she can expect in terms of a mate being judgmental. She may have decided that full disclosure is non-negotiable in a long-term relationship, which IMHO is healthier than a closet full of skeletons.
Second, I never had an upper limit as to what I was willing to deal with in sexual history. I cannot tell you accurately how I would react to a disclosure of 500, or even 100, but I have lain in bed next to a sexual partner (afterwards) who told me tales of other encounters, and I wasn't bothered by even the more sordid ones.
Third, she's apparently been in ltr's recently, so this might just be the sort of thing she got out of her system and has moved on. People change. They make mistakes, and this disclosure might just be the sort of thing that she is tacitly admitting to as a blemish in her past. If she's proud of it - well, that's a bit different.
Fourth, I'm going to assume she showers or bathes from time to time.
So, my humble advice would be to tread carefully but not rule her out tout court.