I've mostly just called her by her first name since I met her, but now my wife wants me to call her "mom". I'm not quite comfortable with that, though, because I love calling my own mother that.
Thoughts?
I call her Karen. It's been 18 years, I don't see that changing.
It took me a long time to have a good relationship with my mother-in-law, years, but I just never could call her "mom". She had a lot of wonderful qualities, but she was not the warmest of women, and fairly judgemental. My father in law, on the other hand, I had a wonderful relationship, and started calling him "Dad" almost right away. Sadly, after having been married to her son for 37 years, she became my EX-mother-in-law, and we have NO relationship now. I hope for you that you can develop a good relationship with your m-i-l, and perhaps come up with a special pet name for her!!