As a long term substitute (12 yrs and counting), I am we'll aware that some parents don't care for substitutes and question our abilities. Blah
The other parent needs to let it go because that attitude with be picked up by her children.
Substitutes, especially long term,are very well trained and we have a higher standard to achieve because if the attitudes of people like your friend. At our school, we are involved with much more than just showing up and babysitting a class. We are active with teacher planning periods, other supporting classes, the administration and of course, parents.
Subbing is something I chose to do a long time ago on the side . Subs don't make much money.... The routine subs you see are there for 1 reason.... We love the children.
I sub when I can because my main job is running my company. Subbing is my outlet to stay connected with simething I love to do and even I'm there, its my "mental break" from my normal day to day which re-energizes me and I am more productive in both areas.
I love the children I work with. They all visit me for Halloween and know they'll get special treats. When I run into them while at grocery or something, they come hug me and tell me about their day. I get paid hardly anything and compared to my real job I am basically volunteering my time. BUT. To me..... It's priceless!
In a perfect world I guess women teachers would schedule getting pregnant so they would not hinder other people who have issues with quality substitutes like your friend does.
Too bad your friend isn't more open minded. Your children are gaining more experience and they will be able to adapt to changes more easily than some students and GASP. ... They learn too!!!