How should I teach my 2 1/2 year old to respect other adults?

My daughter will be 3 years old in a few months and she doesn't listen to other adults (i.e. my sister, her caregiver, the babysitter, my friends) when they tell her to stop misbehaving. If she is around me and she disrespects an adult, I'll explain to her that she's wrong and she doesn't talk to grown ups that way. I don't have a problem with her listening when I'm around but when I'm not around, how do I make sure she listens to other adults?