Y.D.
A. you are not over reacting if I were you I would get a new sitter! and preferably one that has excellent references and is willing to follow your wishes. My son is 17 months old and he naps 2-3 hours during the day as well. Your child needs that sleep. I Hope you find a Good sitter! If you need any info on one I can refer you to one.
Good luck!
Y.