Finding a new travel partner [View all]

My 23yr old daughter and her friend have been planning for the last year an extensive trip to Europe this summer, its now getting time to book flights and make hotel reservations but my daughters friend is now having second thoughts about committing to the trip and its looking like she will back out.
My daughter is not too keen on doing this trip alone and is really disappointed at the prospect of the trip not happening or having to do it alone.
Is there some website she can use to find an alternate traveling buddy?And or if she does have to do it alone perhaps a website on safety recommendations for a 23yr old woman traveling alone in Europe.
Thanks.