She is only 74, but she is very heavy and has difficulty walking. I think she's having symptoms of dementia, too. She can't think of words to call things like keys or a fork. I have to make her shower, and can only get her to shower once every 1-2 weeks, and that's if I strongly insist. She will go to the store about once a month and buys pre-made cakes, brownies, chips, candy. Then, she'll eat only that stuff until it's gone. She goes to bed around 7:30 and sleeps for 12 hours. Then she goes back to bed several times during the day. I would estimate her being in bed 16-20 hours per day. She moans and makes noises like it hurts her to move or walk, or just sitting, but refuses to see a doctor. I've made several appointments, but she refuses. After the first week of not bathing she smells terrible. She will only bathe or change clothes if a MAKE her. Home Health was coming out (not doing much) but they stopped because she will not go to the doctor.
I bet it is very difficult for your Mom to walk if she is very heavy, her knees are probably screaming for deal life. Would your Mom go to a senior center couple times a week to be around people of her own age group? If she likes it, hopefully she will take a bath/shower and put on clothes she really likes. Being around other people is so good for their soul.
As for the grocery shopping... is she driving herself? If not, you get the groceries but don't stock up on sweet things, experience with more healthy stuff like grapes, veggie chips, yogurt... and try to get Mom to do some walking, a couple of laps around the inside of the house at least.
I've tried to get her to go to the senior center. She won't go. She's only left the house 3 times in 4 months, and that was to stock up on cigarettes and all that sugary food. I buy healthy, organic food, never junk. She says she doesn't care that she can't walk very well. She doesn't care that she smells horrific. She just laughs at me when I try to get her to do anything or make suggestions to her. She is perfectly happy sitting in a chair all day watching TV, except for sleeping, which she does a lot. She wants me to wait on her constantly. I think her mind comes and goes. She only flushes the toilet if she defecates, but she gets feces all over the rim and makes no attempt to clean it off. Once, she pooped all over my bathroom floor. She told me she did it, but again, made no attempt to clean it up. She has no interest in doing anything or seeing any family. She's kind of always been that way though. It's really making me crazy that she could do some things for herself, but she does nothing. I carry her dishes to the kitchen, clean her bathroom, do her laundry, etc, etc. It's like she's on vacation, and I'm her maid.
You're not doing her any favors by letting her live the way she's living. If she truly has dementia, now is the time to get her into a facility where there are three shifts of people to care for her. Otherwise, she'll take you down with her. And from the sound of things, she won't care one bit that she's ruining your life too. Save yourself.