What does it mean when a female gives it up on the 1st date?

So before this girl became my gf we went on a date...later that night we had sex...the next morning i was kinda turn off by her cuz she gave it up so "quickly" so went to get advice from a good friend of mine asked what does she think? she told me it could b that she was really feeling u or b careful...so i thought about it an we had great chemistry an hit it off the 1st night we met...then i went back to ask the girl, which is now my gf, y she gave it up so "quickly" she told me it felt right....