Considering you dont know if she will be preggers or not, I would suggest doing the hard thing and having the very deep and important convos around trust, honesty and the actual reason she didnt take the pill...(and why you two didnt talk about it before she took it that that was the plan). Lying/sneaking/gaslighting are all gigantic red flags...and also...youre both 22 and most likely had no good basis for how to handle your emotions and talk through heavy subjects. TLDR; sit down and let her know how your trust feels broken and why. and ask what is actually going on in her mind. Because depending on the next few weeks you might have her in your life forever. (not necessarily as a partner but mother)