OP my MIL is the exact same. Except FIL takes many many business trips during the year and MIL doesn't drive. So not only does she stay with us for days and days, we have to shuffle her around. She has to be picked up, dropped off and taken around for errands. She's in good health and a fairly young 62. She has a drivers license but refuses to drive.

She comes over, expects meals and treats my pantry like a grocery store.

Can't stand it.

OP, it's the generation. My mother has anxiety issues and can't do much on her own. She'll never sit in a coffee house or bookstore alone. It makes her insecure. The most she'll do is go to Bloomingdales by herself. Our generation tends to handle being on our own better than the previous ones. Did MIL go to college and live on her own before marriage? Neither of my parents were on their own, EVER. Went from their parents' house to their house owned as a married couple with nothing else in between. Not even a college dorm. Nowadays, plenty of women have a lot of practice living alone and aren't afraid of it. We buy homes on our own, we travel on our own, we drive country on our own.

IMO, you should probably try to see her as a product of her time and treat her like someone from another country who has very particular customs they must adhere to. No sense in arguing with her. As far her anxiety and how to impacts you and your family, tell your husband if he wants her to stay with you, he has to handle her issues. Other posters are right: she is NOT going to go to therapy. She thinks her fears are justified and anyone who disagrees is being the unreasonable one.

I think you just need to suck it up and deal with her visits.

DIL here, my MIL is always nice enough to come and visit when my husband goes out of town because she knows I hate staying overnight alone for several days. Give her a little grace OP. I'm sure she can be a bit over the top but that's what family is for. Support her in this. It's not everyday that you have to deal with this. Count your blessings and think of this. When you grow old you may need your son and his family for support.

Maybe you could pay someone to stay with her that she knows? Like a young adult relative?

I'm like your MIL. I was fine when I lived in apartments, but once I moved to a house I was scared to be alone-too many entry points. I didn't have a DH so I got a big dog. Maybe you could get MIL a dog. It made me much less fearful.