Guys don't push fast for a relationship. They push fast for sex, and will lie about the relationship thing to get the sex. Total assumption, but I am guessing guys will be like "sure, we are in a relationship", have sex with her and then dump her.

She probably thinks when guys do have sex you will honor the fact you are now committed to her.

Yup, mindreading. but I am pretty good at reading other women's minds.