I say be thankful you still have a DMIL. Mine lived in a MIL apartment in our basement until we lost her in '08. We loved being able to see her whenever we wanted. We often took meals down and had them with her in the family room/ wet bar area down there. She would come up sometimes when her mobility would allow. I miss her very much and would love to be able to do such a small thing as to put her glass in the sink or dishwasher!
I am in no way dogging you, there may be more to the story, but if you to get along, enjoy every minute you can!
You may find yourself in the future picking up a glass and it may bring sweet memories of her or your chats back.
Life is way to short to worry over the little things!...
Penny