The player/parents were obviously not committed to your team and used your team as a rest area. Do you really want a family like this as a part of your team anyway? A few years ago a parent, during a warm-up tourney, tried to show off his kid to me by showing me texts from a coach of another team asking him to jump ship and join her team. It didn't bother me one bit.
If they leave, they leave. Don't be bitter about it. Get another player if you need to and when you get a chance, beat the team she's on.
Len