I had a friend who took against her MIL to be and was touchy and apt to be offended around the woman, who was admittedly, hardly Mother Theresa. It all ended in my friend's husband being cut out of his mother's will and losing his third share in over £1millon, not to mention poor relations between them all when she was alive.
I remember thinking that this was far too high a price to pay for the luxury of playing the victim instead of being tactful and that, to an extent, it served her right.
In my own case my MIL was far ruder and more interfering and intrusive but I forced myself to see things from her point of view. I wasn't, ostensibly, a catch for her middle class son being a working class girl from a divorced, single parent family. Over the years she came to see that as a teacher and a hard working, faithful, respectable, decent person I wasn't the worst choice he could have made.
Over those same years I came to see that my MIL's abrasiveness came from being a very clever, larger than life personality who was thwarted in her choices in life and who needed to be in control. I also saw that both of my in-laws were decent, generous people who wanted the best for us and wished us well.
My own DD has somewhat the same feeings about her b/f's parents who are older and very controlling and old fashioned. However, I have tried to get her to see that they are good people and if the two of them get married I will do my best to see that the MOTG and the FOTG are on the top table both literally and metaphorically for everything to get the marriage off to a good start. A MIL is not just for Christmas. As for squabbling about outfits! Isn't that what teenagers do?