Oh dear, I can understand how you feel, Cheri
Yes, I'm agree that your sitter should ask you first because you are a mother.
I hope you don't mind me for open my opinion on your thread which it relate on "without ask mother for permission first".
Is it first time? If yes, I'm sure that she doesn't mean out of purposely to upset you but want to take care of your children well for you. I know what she doing painly wrong. I'm sure that she or her mother learn their lessons for not do that again in the future. It would be different story if there're SECOND time.
This thread remind me of my MIL.
I would like to give you few examples of many about my MIL.
1. my MIL ordered everything for Danny's christening without ask us first that's time I JUST had Danny in the hospitail. She beleived that Danny should go direct to have christening right way after hospitail to protect "sinn". I told her that we would not do that until we feel ready........ She is sour that we let Danny christening when he was 4 months old.
2. We left one year old Danny to his grandparent for the weekends. MIL got Danny to hairstylist to trim his hair without let us know. We told her in firm way to not do that again in the future unless get our permission first because we are the parents. She said that Danny is also her grandson, too and want to see his hair clean and neat. I asked her to respect us if we as parents have different view as her.
3. my MIL kept on tell us to buy Danny's first shoes before he began walk. I'm disagreed to this because I beleive to have Danny to wear his first shoe AFTER his FIRST walking, not training him with shoe to walk. Guess what, she ignored us to buy a first shoe for Danny and trained him to walk with shoes that's time he was crawler.
4. She ignored our rules and do what she wants with our son which it's last and enough for us after many times. (We planned before I had Danny that she want to look after Danny while I go back to work). I decided to have Danny at Child Minder with the recommend from Children Protection Service instead of trust MIL to watch Danny. It wakes my MIL up and respect us more and more after had my 2nd child.
Those 4 example points, I gave you is disrespectful and ignorant which it's different with your situation. I'm sure that the sitter realize that she made her first mistake to let her daughter to do your son's hair without ask you first. I would suggest you calm down and make peace with them and also forgive their first mistakes and have a good talk with them and also make arrange with them before you go away again when you know that she is good sitter in the past. Remember that every make mistakes.