Held Hostage by my Mother-in-Law

Every second Sunday, the children and I go into the city for a club to which they belong; this has been going on for years. The matriarch came downstairs today and told me her sister-in-law was coming for tea on Sunday. Thus, I have to stay home. My husband is working and is unavailable. I don't mind missing the trip down to the city and the kids don't mind missing their club; however, I resent the fact the matriarch took it for granted I would stay home, serve tea and make a cake. Yes, this visit is not a simple visit. The matriarch is so pleased her sister-in-law is coming for tea and already anticipates the possible dates when she can go to stay with her in-laws. It is terrible to feel so conflicted about a nice thing but it is worse to be taken for granted. I am not the matriarch's servant but as her blindness gets worse and she relies on me more and more I begin to feel taken for granted. And, yet, I know she is not incapable; the woman will get what she wants and needs when I am not around. But, similar to my children when they were babies, I almost know what she wants all the time and she has tended to stop asking me to do or get things; it is as though she knows that I know already what she wants. Uncomfortable as my husband is with this reality, he has noticed it, too. However, he defends her actions with the idea she won't be around forever. The matriarch has been here almost 2 years, the woman is approaching 99; it strikes me this anxiety is not going to go away. To make matters worse, I feel guilty for having the anxiety precisely because the matriarch is almost 99 and going blind and deaf.