I have been with my DH for 47 years. When we first met, his family were not very nice to me. My MIL was a very nice person to others, but I could not warm to her because of how she was years ago, I didn't feel that she was sincere towards me, and I know she talked about me to other people, because they told me. However, she died last year and I felt that there were things that I should have said, but never did. I can't help feeling some regret about that. I would say act now, as it may be too late to show your appreciation.