Did it impede the catcher's ability to make a play on anyone? (seems like a more relevant detail than the batter's handedness )
I think my immediate call would be "OUCH!" (more likely a choice word, but same effect).
There isn't enough information here. On top of likely being a "had to be there" moment, were there runners on base? If nobody was on, it is nothing. If runners were on and there was a play to be made, the batter is out on the interference and runners return (NFHS). I'll have to grab my USA book, but I'm fairly certain it is the same.
NFHS Baseball has a specific type of interference called follow-through interference and actually has a different set of penalties, but that does not exist in softball.
It was a dropped third strike so catcher couldn't make the throw to first.
Throwing the bat is a non-issue. Interference is an issue. Intentional throwing is an issue.
Most codes do not have any specific wording on throwing the bat.