Don't say anything. Go to the Saturday tryout. If she gets an offer on the spot, take it and then call current HC that evening. If not, go to your current team's tryout on Sunday. Two tips:
1. Wear school uniform (or other random tshirt) to Sat. tryout. NOT current team jersey. Trust me on this.
2. If you don't get an immediate offer on Sat., text that team's HC Sat. evening expressing how much DD liked them/the team and how you would immediately accept an offer should one be given.
Word does travel, but it may not travel quite as fast if you follow Tip #1.
P.S.-You do mean Saturday as in tomorrow, right? Not the following Saturday?
Totally agree with the first paragraph.
And want to add that this is about what team your DD plays on. That's the important part here. Yes, you want to be fair and cool and not burn bridges. But just by posting here you show you'll handle it better than the majority of people. Coaches have seen all kinds of craziness and however you handle it will pale in comparison.