4 "hit-by-pitch" fast balls in a row!

[Steve M]

Unless the rules of the sanctioning body say something else, a pitcher's ability or lack of ability to throw strikes is not something I have any say over. If I think the pitcher is intentionally throwing at batters, I'll take action. If she is just a lousy pitcher, I'm likely in for a long game.
If the rules of the game say there is a limit to the number of batters who can be unintentionally hit by a pitch, then you have a rule to cover it. Otherwise, ya go no valid umpiring reason to take any action.