What do I do about my friend?

[Joanna]

She dated a guy friend (my exchange partner) of mine…. And they broke up. Well, he does not know that they've broken up. When she first met him, she seemed like she was completely fallen for him. He told her he loved her 2 weeks before he left the country, and during the time that they dated, she kept going on about how it was the first time she felt that way about someone/first time her crush liked her back. I kind of turned a blind eye on the whole thing (Yeah, now I feel guilty) because they really seemed to like each other.
Then he left. She started bitching about him (calling him too clingy) a week later. Within a month, she had already "fallen in love" with 2 new guys, and had dated them (Still dating one of them). I chatted with the guy on Facebook a while back and hinted at their break-up, but he said they were still dating. I just decided not to comment on that.
My friend seems to have completely forgotten about him, and is now blabbing on about some new guy (To be honest, my exchange partner was waaaay better looking than her new boyfriends). We have to go stay with the exchange students in another month, and I think things will be awkward for me because my exchange partner keeps asking me questions about her.
I worried for my friend because I've noticed that she always seems to have a new guy in her life. (I met her only this year, and when I asked her how many guys she had dated, she said 8. And this is in a span of 2 years). Is something wrong with her? I've never seen anyone act as desperate for guys as her. (The bit about her being desperate is another story involving a lot of inappropriately touching guys, making sexual remarks etc.)
The weird part is that when there are no guys around, she is one of the MOST level-headed and witty people I know.
(Oh, she is 17yrs old)

[anonymous]

just leave her alone.
her love business has nothing to do with your life and if she is that desperate, then let it be that way. relax, don't care so much especially to others.