Wildsky, I think the solution is simple, have a hart-to-hart with your MIL. Establish some house guidelines and inform her that every family member must contribute to the whole. People love to be needed and to contribute. She only needs guidance, and many minor choirs can be re-distributed to her.
You mentioned that she liked to sew. give her all your sewing.
You mentioned she was at your "play" computer because of the chair. Change the furniture around.
You mentioned that she watched lousy TV shows; Suggest that you both share the cost of a new TV and place it in the guest room for her visits along with that "computer" chair that she is capable of getting out of.
To me, when you marry someone, you marry their family and all of those vows apply to both spouse and family. The exception being, if the spouse has signed-off on their own family members for some reason. You love this man, your husband, this woman raised him, loved him, diapered him, took care of him when he was sick... In her golden years, she just wants to be near him and his children...
One day, you, too will be a MIL. Treat this woman the way you would want to be treated. If you talk to her with love and kindness, and express the truth, and work around the difficulties... you will find that, though your mother has passed on, that you will have a loving dear friend in the woman who bore and raised your dear hubby.
My MIL passed on while my hubby and I were divorced (we still are divorced, but I have cared for him ever since his bad stroke this last August.)... I give her a halo
through all the good and bad times hubby and I had, and her love for our children was unquestionable.