I set her up with a dongle modem plugged into a usb charger plug and located it at a window. I installed a Three pre-loaded 500Gb data sim (£19) which should last a few months. However data download is only around 1Mps. A kindly neighbour, who has high speed broadband, gave her a guest access to his system. It wasn't a great success to begin with but I have now added a WiFi extender and she is getting above 10Mps around her flat.
This will have to do until Openreach figure out how to connect the fibre in the street outside to the building.