She cannot have it both ways. If her bills are excessively high, and they certainly sound it, she is going to have to get someone to help her and that will mean showing bills, talking about how appliances are used and also to consider improvements to the insulation of her home.
If she doesn't want to let anyone in the house to look and will not discuss her bills and how she uses equipment then she will just have to continue paying large bills. There is no alternative.
Assuming she will accept some help, she should contact her electricity supplier. Register on their vulnerable customers register and talk to them. The other place for help is Age UK (previously Age Concern). Here is a link the Age UK Fact Sheet on Heating and Energy [[https://www.ageuk.org.uk/globalassets/age-uk/documents/factsheets/fs1_help_with_heating_costs_fcs.pdf}}
I assume she does not use a computer so either print it out yourself and give it to her or ask your local Age Uk whether they can let you have a paper copy.
My personal suspicion is that she has an immersion heater that is on 24/7 and may not be properly insulated and that she has never changed her energy supplier and is paying the Standard Variable Rate, whch can lead to substantially higher bills.