Our DiL was extremely unpleasant for about 5 years after she got together with our DS - refused to join family parties, rude to our friends, jealous of the relationship our DS had with his sister - I could go on. And on. It upset us very much.
I think she was very unhappy and insecure, thousands of miles from her own home and family, which she had fled. But gradually, although nothing was said aloud, as she and our DS became established in their lives (careers, house, no children by choice) she has changed and is invariably pleasant and polite, if not very sociable.
Mummymoo2015, if you feel the need to apologise, I think your MiL would accept it gladly. But change your attitude too! As has been said, actions speak louder than words.