Yeah...unless you're at the upper reaches of 10U competitive ball, any fly ball to the OF is an adventure. I do remember a near-miracle catch made by a 10U REC right-fielder against a tournament team that WON a game. Whenever I run into her, I mention it and get a huge grin. Heck, I know an older pitcher who can't seem to buy a break in RF. Every time I watch her pitch, a lazy fly ball to RF gets dropped, and runs score.
Fly ball to RF is a tough play... RF should be a set position. Not a fielder who plays LF and CF. Sliced balls from RH batters in RF is one of the hardest catches to make in softball. Plus, like other have said, throwing from RF is crucial, going to 3rd should not be automatic.