Has your husband spoken with her? He needs to step up and find out what on earth is going on. He also needs to remind "Mom" that he will always be on your side on this and so if she does not spit out what is going on, he is not going to be pleased with her.
This is ridiculous behavior. Is she ill? Is she going through a change of life? Is she depressed? Does the rest of the family stay in touch with you?
Get your husband to speak with his parents and if this cannot be solved, you and your husband have a discussion waiting to happen abut how you want to proceed.
Here is my story. After 25 years of marriage, I told my MIL and SIL I was done with them. I sent them a letter very clearly stating my issues with them. I included emails from them so that I could prove my point. They had treated my husband terribly for all of the years I had been with him (we met in middle school) and I told them the final straw was the fact that they ignored our daughter for all of her school years and blamed me for not informing them of her activities. They always seemed to assume the worst from me.
With as much as I post on here, you can imagine that was a joke!
I then informed them that I was going to encourage my husband and daughter to continue to love and go and visit them, but I was no longer going to be witness to their behaviors with my loved ones.
My husband spoke with his mother and sister. He told them he was on my side and always would be. That he was disappointed with their treatment of me and reminded them of all of the things I had done for their family including the care of their parents, the organization of so many family events. The cheering on of their endeavors for all of these years.
I must admit, I am sorry it came to this, but I do not deserve their treatment of me.
I practically have to force my husband and daughter to go and visit them.. How sad is that?
And so I encourage you all to figure this out. My husband and his mother went to counseling together and she admitted she "has always favored her daughter, but that moms are always closer to their daughters" The counselor said, "no that is your choice."
I am the one ths family expected to care for his mother.. I "took such great care of the grandparents".. So much fo r hat plan.