Step Daughter doesn't love me

Well we recently had the babysitter tell us that Amelia has been talking back and flat our rude to her babysitter. That she calls her names and disrespects her by mocking her and insulting her. 

This was a huge pill to swallow. Amelia NEVER acts like this around us. But honestly, that doesn't matter. The fact that she does this when we are not around is alarming. Her mother, my husband, and I have all agreed to work harder on monitoring her behavior and teaching her better manners. 

Well I seem to be the only one holding up my end of my bargain. I am correcting her demands and having her change them into polite requests. I am making sure that she understands her jokes can come off mean and insensitive. I am teacher her to hold open doors for others and how to be more independent rather than expecting things to be done for her. 

Well now she hates me. She avoids me at all costs and has recently stopped telling me she loves me. I tell her all the time I love her and she goes silent. I am too embarrassed to ask her why she won't say it back. I don't want to force her to say it back because it's the "polite" thing to do. But man. This is tough. Do you think I am being too hard and that's why she won't say it?