My opinion would be that the NFHS sometimes overdoes it with some of their rule interpretations. Sometimes they try to legislate fairness into their rules and that creates rulings that go against the rest of the softball world.
Back a few years ago, they came out with a ruling that on a walk, the three-foot running lane rule is to be enforced- even though a throw to first in this situation is NOT an attempt to retire a player. It can be a common strategy to stop a walked batter from rounding first, especially if there is a runner on third base. But if you throw to first following a walk, you certainly are not trying to make an out on the walked batter, who is entitled to advance to first without being put out.
This is just one of several plays where they have expanded the running lane rule to cover plays that it was not originally intended to cover. For instance, they have another interpretation where a batter-runner is advancing to first base, is put out, then is hit by a throw to the plate while out of the running lane, calling this interference. This is an interpretation that has never been used by any other santioning body. The rule covering the running lane clearly states that it applies when a runner interferes with a fielder at first base who is receiving a throw.
I guess that their message is "We really, really want runners to stay inside the three-foot running lane, no matter what". But with these interpretations they have expanded the interpretation of the running lane beyond what it was originally intended to address- the defense trying to retire a runner at first base.
Now, if the catcher makes a throw that the umpire judges was an attempt to purposely hit the batter-runner, rather than to field the ball to a fielder at first base, you should not rule it interference. If the umpire judges that the throw was not "to the fielder", but "at the runner" with the intent to hit her, and interference is not called, the defense runs the risk of causing a loose ball that will allow other runners to continue advancing. Also, depending on the severity of the infraction, you could be looking at an unsportsmanlike conduct or even malicious contact ejection on the catcher.
To be interference, the throw would have to be in the direction and vicinity of the fielder taking the throw, such that the throw would have a reasonable chance of actually being caught. If the throw IS "to the fielder" and the batter-runner IS out of the running lane, it definitely IS interference. If the batter-runner gets hit in that case, it's her own fault for being out of the lane.
Of course, if the throw hits the batter-runner while she is inside the running lane it should never be called as interference. Live ball, play on.
Again, these are interpretations for high school play only. They will not apply to other sanctioning bodies, like ASA. Personally, I don't really care for them, but if I'm working a high school game I'm bound to follow them.