I'm not understanding what is not fair about the sub being paid? It is hard work and she deserves to be paid and yes, it is lower than teacher's salaries (maybe higher than para salary?).

I agree with the person above who said to suggest that the sub teacher enlist the help of parent volunteers. Kindergarten parents are generally very willing to help.

I'd keep my distance from this situation and not offer any more advice. If the two of them can't come to a solution on their own, then they can choose to have the principal mediate. You are sacrificing your own professionalism by getting involved.

Just my two cents.