Why did she suddenly change towards me?

My cousin’s doughter has been too close to me. She is about 15 and I’m in my 20’s. I live far from them but we had a family vacation. On our vacation, she was too sweet to me. She even let me cuddle her a few times. There was a time that she was sleeping on me, embraced my hand and put it on her breast. I did not react because I was’nt sure if she knows what she was doing. In short, she was always finding a way to touch me. She was sweet to me since she was 12 when I visit her once a year. We were so sweet the whole week in our vacation but when spend time in my moms house everything changed. She even called me a pervert because I slept with her once even I did not touch her private parts but before we slept she said there is no problem if I sleep with her. We also had some fights and she was not sweet anymore. Then I went to my house and she followed with her mom a week later. We fought almost everyday but always reconcile but never been sweet again. I know when we were so sweet her mom was looking at us differently. On there last night they checked out from the hotel and spent a night in my room. I slept on the floor and let them sleep on my bed but when she woke up she asked me why did I sleep on the floor while there is still space on my bed? I did not answer but of course I don’t want her to call me a pervert again. Now that they’re gone my question is what do you think the reason that she was so sweet but all a sudden changed. It will be hard for me to ask her because she does’nt like talking on the phone. Please advice…