Why did she change?

This girl I knew for 4 years really liked me.. and I like her. She has a bf and decided to flirt with me, we really hit it off me and her.. However when her friends started asking her if she liked me she always told them no. I talked to her and she admitted she did like me however she did not want her friends to know because she said they will talk behind her back. Anyway after that night its not been 5 days and she is totally different with me now, she is super cold and doesnt flirt anymore and doesnt call me as much any more.. What is going on.. I feel very hurt.

She told she is hurt because they found out and that I told her that she couldnt keep stringing me along while she was dating someone.