I had surgery to repair a broken wrist on my dominant hand. I was firmly casted to just past the middle joints of my fingers and thumb. Writing was an experience. Learning to wipe my tushie left handed took a bit of coordination as did learning to pull up my pants, button my jeans, drive my car, tie my shoes, you name it. Almost everything you do is affected. It's inconvenient but most people are very helpful when they see the cast. I didn't find that the pain lasted all that long. I wore the stiff cast for 3 weeks and a less restrictive one for another 4 weeks.
Aside from personal hygeine, the biggest problem for me was food preparation. Opening a can, cutting anything, pouring anything, was all kind of tough. For the first few days, my mom or whoever was helping me draped a towel around my neck when I ate because I seemed to get more on me than in me until I got better at eating left handed

I lived on microwave foods and cereal bars so I'd suggest a LOT of help in those areas. Also, your mom's friend of course may be totally different but my wrist was quite weak for a long time. Help carrying heavy groceries and with heavy cleaning chores like cleaning the tub was needed for a few months.
I would suggest to your mom not to wait for her friend to ask, just jump in. A lot of times we don't like to ask for help because we don't want to burden people or be a pain. Especially something like this that may require a lot of intimate assistance in the beginning. After a couple of days at home, watch, and if she seems to be struggling, just say "here, let me help you with that". Some she'll learn to do on her own quickly like pulling her pants up and some she really should just let someone else worry about, like cleaning the tub.
We are actually quite adaptable and just about the time she gets to where she can do pretty much anything she'll be out of the cast. Then the real fun starts with the PT
