It depends...how far is the ball away is it right in front of her? is it 10 feet away? what's the score tied last inning? are you up by 5 in last inning.
It is always hard to access without understanding EVERYTHING in the situation sometimes outs are paramount, sometimes runs are paramount.
As a general rule at 12U your catcher and first should be able to execute this say over 50% of the time and get 2 outs (yeah I am just making up a number but better than 1 out of 2 sounds right but probably not better than 2 out of 3). Biggest variable is obviously the ability of the players involved the catcher, the first baseman and the runner. A good runner might be more than a third of the way to home after catcher checks she might stop but not retreat at which point the catcher need to know whether the out or run is more important. If your 1B and C are awesome studs and the runner at third is slow they might do this in their sleep 4 out of 5 times.
Ultimately this is one of those things where not enough kids have the softball IQ to understand whether the run or out is more important, I pretty much take this out of the equation for my players GET THE OUT unless I tell you otherwise.