Hygienist called in sick for the 4th Monday in a row

I know people get sick, but this is getting ridiculous. Every Monday for the past month, my hygienist calls in "sick." I'm starting to think it's not a coincidence. I'm stuck seeing her patients or rescheduling them, which makes me look bad. The owner won't do anything because "we're short-staffed" and can't afford to lose her. I'm so frustrated. I can't run a practice like this.