She has rules, you have rules too.
Iron Rule of Tomassi #3:
Any woman who overtly makes you wait for sex, or implies by her actions that she is making you wait for sex; the sex is never worth the wait.
You are not her highest priority; there are other considerations she is observing in light of her changing one of her rules. Regadless of whether or not this change was prompted by a pregnancy scare or some other reasoning, the rule has changed. Her desire to be intimate with you has been superceded by some higher priority.
Play this out to it's logical conclusion; for sake of argument lets say you did convince her have sex with you after implicitly telling you she was now 'saving' herself for marriage. It's you that will now be the villain for 'tempting' and 'coercing' her into having sex with you after her virtuous protesting. Do you really want to be with a girl who's impulse is to resist you rather than desire you?
Or play this scenario out; You decide to obey 'her rules' and maintain the relationship in as sterile a form as you can, by repressing your sexual impulse for as long as it takes for her to 'come around'. How long do you think you could hold out? Because essentially you are making a bet with her that you can remain celibate and faithful for as long as she deems necessary for her to marry you. How long would you forego your sexuality to prove worth to this woman?
And the last possibility is that you will indeed marry this girl and have 'legitimate' sex with her in the future. Can you honestly say that this woman is worth the sacrifice in light of the fact that her impulse is to resist rather than desire you?
As we're so fond of reminding ourselves here, women will fvck. They might not fvck me, they might not fvck you, but they'll fvck the guy that they have an intense desire to fvck, convictions be damned. A woman who wants to have sex with you WIILL find a way and means to do so. She'll relocate across the country, crawl under barbed wire, avoid the suspicious wife and crawl out a bathroom window if she has a genuine desire to knock it out with you. This girl had that desire at some point as evidenced by her former behavior, but obviously no longer feels that intense motivation to put off her convictions because her convictions outweigh her desire to break them for you. In light of this, do you honestly think that any sex you could convince her to have with you, whether married or not, would be to the same degree of passion as when she was previously motivated by her genuine desire?
Don't waste your time. How long would you wait before selling if you owned stock in a company that consistently lost value quarter after quarter? Do you wait till they go bankrupt? No, you cut your loses, sell it off and reinvest in better prospective stocks that return a dividend. Spin more plates.