i have the same prob... bf's mom at first I thought she likes me because she's treating me well when I visit them at home but there was this one time I changed my cellphone no. and sent a group message including the mom, she replied as if she didn't care about my new number. So I replied and explained that that text was just FYI.
Then she replied with harsh words, telling me to stop bothering her and all. But I couldn't refrain myself from not responding back, I asked in a very respectful way, why she's like that to me. (Because there was also an incident that I sent her an inspirational message and she replied very badly, but then she said sorry afterwards.)
Her reply was worse, including bad words. I texted her back and told her that I respect her like my own parents but also to respect me as a person. I told her nobody ever treated me that way, not even my parents. I was so angry at her but I tried to reply still with respect, not like fighting back.
That happened last year but until now I haven't got any sorry from her. I never texted her again or visited their house. I still gave presents last Christmas but never received a thank you from her. I know I forgave her already but I think I could never forget what she did and said to me.
Now, it's also affecting the relationship with bf. I think I couldn't bare to have a MIL like her and often the reason why we fight is because of her. I don't know what to do...

sorry long story, just wanted to let this out...