Boyfriends mom..

My boyfriend is native American (Osage tribe) & I'm white, his mom acts like a civilized human to me, she treats me with more respect than she treats her own family, but in the past she has gotten mad at me & called me a white bitch, which really offended me, my boyfriend and I talked to her about it, telling her it offended me, and she apologized...

But, yesterday, I was talking to his sister and she told me that their mom STILL called me rude names behind my back. I don't get it, I try so hard to be nice to her. I do everything I can for them and I still am not respected. I love my boyfriend and his family so much, I just can't deal with his mom.

What would you all suggest I do?? It's hard to ignore when she's racist toward me... i just want to be accepted by her!! Sorry if this seems like I'm rambling, I'm just so hurt by her actions. :(