"Need to change and want to change. But how can I not care about what MIL says?!!!"
Part of it is detaching "her" from the words - think of it as she says what she says because she has not been brought up the same way as you perhaps. She may have had a horrid childhood, she may just have had a bad day, either way, she has crap going on in her life that means that she does not see the world the same way as you do,
so you cannot expect her to respond the way you would like her to, because she does not know how you would like her to respond, or has not got the tools at her disposal to do so.
I work in a health setting and we get lots of grumpy people in, some are nasty, some are nice. Looking at it from my angle (as a contented person) they are ill, in pain or dealing with someone who is ill or in pain - that will colour their dealings with others - they came in on a bad day, I try to make it a bit better. Sometimes it helps, sometimes it does not.
Their angry words are not aimed at me, but at their inability to get what they want.