Oh, my heart aches for her. I think most of us have had this happen to us at least once.
My hubby always says his daughters can't date until they are 29, then they can marry when they are 30....he says it's because he remembers what he was like as a boy/young man. The reality good parents can't shelter their children from all pain, so we have to teach them to cope in strengthening healthy ways.
None of us know all the answers, but I had figured out by about 25, than any guy who went overboard right off the bat, put me way up on a pedestal, and showered me with all the good stuff immediately was going to be trouble in a fairly short amount of time.
Usually they were:
A. doing all this to prove they were really over someone else (I think this is what happened for your daughter).
B. were trying to create the appearance of love, because they wanted it so badly, and were not really getting to know who I actually was.
C. going to soon use those "gifts" as ways to try to control and manipulate me....they were conditional.
None of those things are a healthy relationship for anyone. And there is no way at 17 that she could know those things. It took me a decade to even have a clue.
Explain to her that empty feeling in her right now heals best when she takes charge of it and rebuilds it. That God has designed us to heal, and real confidence work this way:
Self esteem is something that others can shake and tear down, because we base it on what others think of us. Self respect comes from within, from knowledge that we can do great things, right things, with the strengths and talents that God has given us, and no one can take that away, because those accomplishments come from us through God.
Her heart is breaking, and this may not help, but my prayers come with this post.

And through God she will heal.