There are compelling reasons to keep the peace with a DIL.
My son and daughter-in-law bought a sailboat and put it in a lake halfway between their home and ours. Our son was deployed for a year during which time our DIL never spoke to us. We couldn't even see the children at all, even though we tried.
When son came home, she acted like everything was fine. Now he's gone for another year and the marina had storm damage -- so whom does she call? Not her folks, who she has over to play on the boat all the time, but us.
I told husband, "Nope, I'm not doing it." He's like, "Oh, she's a sweet girl and needs our help." I think she's a sneaky, two-faced ----- (I'm biting my tongue off here.)
So, do I go along and help or beg off? We're older and can easily cite health concerns.
Although this isn't a friendship problem, per se, the relationship between mothers-in-law and daughters-in-law is a tricky one. Your son's deployment has to be difficult on everyone, especially his wife -- but your DIL's behavior towards you and your husband makes me shudder. That said, I still think you want to give her every benefit of the doubt because she is your son's wife and the mother of your grandchildren.
If you alienate her completely, your losses can be great. And putting your son in the middle of his parents and his wife is also a no-win situation.
It sounds like the storm damage is is a once-in-a-blue-moon situation. If you can possibly afford to help her, try to do so. It can't be easy for her to have her husband away for a year. Hopefully, when he returns home for good, she'll get closer to you and your husband. Don't give her an excuse not to.
P.S. You may be interested in reading an article on recent research on mothers-in-law that I wrote for Life Goes Strong.
Follow Dr. Irene S. Levine on Twitter: www.twitter.com/moretime2travel