There is a possible way, but it is not easy nor is it guaranteed.
If grandmother has a relative in Europe who is an EEA national - or a UK national who is willing to move their '
centre of life' to another Union memberstate then grandmother may be able to join them there.
Note if someone volunteers to go to Europe from UK to do this then their whole immediate family has to go with them too, not just the volunteer.
Preferred valid relatives can be child or grandchild so that grandmother is a
direct family member of the sponsor.
This is called the
Surinder Singh route.
Having established yourselves in Europe and established dependency by virtue of the EEA national/Brit working and grandmother residing together, you may after some months 'decide' to return to UK.
In this way, grandmother returns to UK on the EU migration route because the BC has become a
proxy EEA national.
Ofcourse there may be issues of disruption, health care, acclimatisaton and language - but surely no worse that present conditions.
There are Anglophile and English-speaking countries in Europe; eg Eire, Malta (possibly Cyprus) spring to mind.
You can get up to speed on
Surinder Singh here:
https://www.freemovement.org.uk/surinde ... ion-route/
Note this route may or may not exist in its present or any form after
Brexit. But faced with the stark alternative of no UK visa then maybe its worth at least looking into.