Disclaimer : I still = noob.
From experience after frustratingly trying to make her work, her charge bats spread out too awkwardly, and makes it too inconsistent to hit (even when I stand right in front of them).
Charging didn't seem to increase the size to me (but it might, not sure). It does increase the amount of bats released, but I'm pretty sure you knew that already. The bats have very little to no homing (pretty sure none).
Charging the bat also sometimes has this weird delay, where even when you let go it doesn't fire, which is quite irritating.
The counterbat is easier to "activate" than mellow's counter in some cases (since all you do is hit it and wait for them to hit you, not dash around trying to hit the melee attacks), but it's much weaker since it doesn't knock the opponents up, and they can just keep going with their combo.
Her bats scale off of tec, pretty sure.
Edit: Oh. I have no clue if tuning STR would increase the size. It'd be really broken if it did.. but now i wanna try it.
I had some kind of success just going hopper with it, but still, it's.. not as good as mellow.