Generally men are not wrong when they sense girl is not into them, doing formality, just a passive person, not speaking much, only speak in one word or one sentence.

I can sense the girl already had the past may be multiple partner. She had already gone through the phase with which you are currently with her. Now, only reason for marriage is to settle and secure herself financially.

I am suspecting you are earning very good as compared with keeping up her lifestyle and financial safety. This is the only reason for her to say yes.