Need advice about being with my friends ex

I'm a college student. Last night, I was hanging out with a few friends, partying and drinking casually. There was a boy there named John. John and I were being really flirty and really hitting it off. Then, some people invited a few other girls to come over. One of those girls, Alexandra, had a casual relationship with John which ended a few weeks ago. Alexandra and I are friends, we are not close friends, but we are friendly. She is in my sorority, so inevitably be seeing her a lot. She pulled me over after seeing that John and I were being flirty and said "don't get with him." I told her that I didn't understand her reasoning; they were not longer a thing. As the night went on, we both kept drinking, and John told her that he is completely uninterested in her and since they ended their casual "fling" a few weeks ago, that was that. He explained that he had no right to control who he can and can't hookup with. Alexandra proceeded to go upstairs and lay in John's bed. He went upstairs and told her to get out. She refused and said things like "I'm sleeping here, come get in bed with me, I'm not getting out of this bed." He was get frustrated so I told her I'd sleep with her downstairs on the couch because that was the only thing I could think of to make her think I wasn't going to hookup with him. She held me hostage and every time I attempted to stand u0p to go to John's room she would wake up and not let me move. Finally, she fell asleep and I went to John's room. We woke up the next day and Alexandra was gone. She stole my shoes and took her with them. I haven't spoken to her since. John and I are on good terms. I am not a confrontational person and I know I will be seeing her all the time in my sorority. John and I are on good terms, we ate breakfast this morning. I need advice. Should I ignore the situation and wait until I see Alexandra and see how it goes? We were both drunk, maybe she doesn't remember. Also, should I say anything to John about it?