there is absolutely NO way she can tell the very next day after having sex that shes pregnant...but given your circumstances she very well could be but she wont know until shes misses her period or takes a pregnancy test..the pregnancy test can be taken 2 weeks after shes had sex or she can wait for her period and if she misses it test...but theres no way she knows now

First rule of sex as a male: ALWAYS WEAR A CONDOM.
First rule of having sex with a woman when you are a male: If the girl says she is 'safe' STILL ALWAYS WEAR A CONDOM!

Now, the likelihood of her knowing she is pregnant will not happen until she misses her period. If she says she is pregnant now, she is messing with you. She is probably frightened too though, so have some compassion. You two had sex together, so both of you would be 'to blame' if anything happened.

RUN out and get some condoms. NOW.