I would not suggest melatonin - it has not been tested on kids. We looked into that as we use it. Both sets of our parents live outside of the US, hence we have taken many plane trips. I would say that with the big time change your daughter will WANT and CRAVE sleep. We just make sure that they do sleep some on the plane, and when you get to where you are going, unless it is night, do not let her sleep until it is sleep time.
Good luck, sounds sorta fun!!!