I wish I could contirbute to the pictures...my photochop-fu is weak.
But, you need to talk to the school's amdinistrators about the whole pickup the kid issue.
My sister and I are each on the "emergency contact" cards for each other's daughter at their respective schools. If I need to pickup my neice at any time, for any reason, on any day at her school, I simply walk into the office, they pull her card, and call the room to send her to the office.
Same goes for my daughter and my sister. The teachers, or anyone else ARE NOT INVOLVED and have no say WHATSOEVER in the process. It is between me and the office staff who is in the office when I walk in.
If the schools in your area do not have such a thing, then you need to have your sister write a letter to be put in the kid's file and signed by the school principal as a witness, that you are allowed to pickup at anytime, anyday, for any reason withot contact from the mother.
My sister calls me and says "go get her"....I go, no problems. Also, if for some reason the school can't get ahold of my sister, they call me next. and vice-versa.
No Expert