This is something we were turned onto by DD's initial pitching coach. His [strong] opinion is that young girls are done a disservice by not being taught how to play catch underhand. And that it is a big cause for the lack of pitchers in the game. I've grown to agree and be a big supporter of underhand catch.
Even though DD quit pitching full time, we still do underhand catch and long toss. For one, it's fun and different. But keeps her just enough in pitching shape that she feels comfortable if called to emergency throw or eat an inning.
Problem is that us rec coaches start with our little daughters and frankly have no idea what we're doing. We just assume the fact we played baseball when we were 14 and follow the Yankees, along with help from YouTube, will be enough to coach a team.