Need help finding title and author of holocaust/future book?

The book is about a girl who is from the present time. A holocaust survivor visits her school. Then the girl seems to go back in time but she's a different person. It's the holocaust time period. The girl goes back and forth between past and present. and either writes, finds or places one of those anonymous pamphlets left on park benches. then she's in some gathering place or something had been round up at a sleepover, could only pack one suitcase... there she meets the survivor who went to her school. Then she's in the present and finds out the ladies dead. she goes to the memorial service or something and sees the pamphlet. If you could help me figure out the name of this book that would be great. I've been craving it.