How approachable is she about the reasons for feeling lonely. The solution will be very different and dependant on her outlook.
Does not know what is available in her area.
Physically or mentally unable to leave the house
Does not want to put the effort into finding activities
Thinks that other should come to her
Is shy and nervous in new situations.
Does not want to impose or be a nuisance.
Some areas have Red Cross, WVS or local charities who visit people who are unable to leave their house.
Local Libraries often have knitting or reading groups . They advertise Walks and meetings too
Lots of churches run coffee mornings, there she will meet all sorts of people and she might find out about doing some voluntary work.
U3A offer opportunities for people to get together
Local Authority websites have details of groups.
If she does not want to go out, she could maybe start a hobby, cross stitch, painting, jigsaw, Scrapbooking etc. I know this is not providing company, but it will occupy her mind and make the time go quicker. If she knits or crochet lots of charities want squares.
Finally maybe have a look at Gransnet. A lot of local Groups set up meetings. If she can get to East London, I belong to a lovely group where she will be very welcome. PM me if you want to know the details and I will be happy to take her along. There are only 5 of us all aged 65 plus.