About why it happened, I have asked in the past in the very same forum, why can this happen! The answer shocked me as it was so real!
The reason why it may have happened is that you made her feel like a slut!
For example, if you tell a woman to come over to your place and have sex she will propably reject you even if she likes you, cause that way she looks like a slut,
BUT
If you tell a woman, to come over to your place, to show her your new aquarium (which is stupid actually cause you both know you're gonna have sex) she's gonna come! Why?
Because in her head, she'll think, "I'm not a slut", I went for the aquarium after all! She'll be ok with it no matter stupid it actually is!
So, maybe you did that! And she had to come to THAT point (completely naked) to understand that she is being a slut!