Difficult DIL- time to deal with it?

My DIL has, over the last ten years, become more and more cold and prickly towards me and my DH. Very occasionally after we’ve met I’ve said to my son, was A ok yesterday? She seemed a bit quiet. And he’s just said, yes fine. He had also grown much more formal and distant towards us. She can be perfectly charming to other family members, who have also noticed the way she treats us. They have three sons. I am a very sensitive person who hates any kind of upset or atmosphere and over the years I’ve bent over backwards to be friendly and welcoming but lately I’ve become obsessed with this situation and it’s causing problems between me and DH because I obviously want to see the GC but he groans every time I suggest inviting them over because he hates the sour atmosphere and has to bite his tongue because I beg him not to rock the boat. What do other folk think-especially anyone with a counselling type background? Should I ask to meet her for a coffee and say that I think it’s important that we get along and is there any more I could do to help out with the boys? I certainly don’t want to start listing all the times she’s been weird with us and neither do I want start by asking her if we’ve done anything to upset her. We treated them recently to a long weekend away with us which was a nightmare. ( they go away regularly with her parents). She was moody, abrupt, bad tempered and obviously did not want to be there. I think that is what has brought matters to a head.