Many of us have 'been there and got the tee-shirt', so you are not alone!
I used to type and print out simple numbered instructions for any devices, i.e. 'Washing Machine':. 1. Open door, 2. Put in washing, 3. Close door, 4. Put powder in pull out drawer, 5. Turn knob to '3', 6. Wait until machine stops etc, etc
I laminated each instruction sheet so they were durable.
I did this for the television, telephone, washing machine, TV remote control and even, in the end, kettle. It is sad to witness the decline of a very intelligent being, is it not?
With regard to the telephone and doorbell, I was able to access items made for the hard of hearing, so, the doorbell would flash if rung and the telephone was especially loud.
I am afraid that this was all more than twenty years ago so I can't be positive but I think the local authority provided these things
Please also consider contacting 'Action on Hearing Loss' {I think) who have good ideas and practical information for those hard of hearing.
Finally, the BP machine... I agree with others that you will have to buy one and when you use it with her, encourage her to be able to manage on her own. You could make up a chart, so she can fill in her own readings. That may encourage her.
Others have suggested you write to your mother and that's a good suggestion. I would type and print it out then give it to her along with some newspaper cuttings regarding C-19 to explain the situation.
I hope things improve for you both.