Realistic countries need to process citizenship for former EU citizens who have been living in their country for long enough to achieve citizenship.
It'll take them more effort, but after living in France for long enough to lose UK voting rights I should hope that the rest of the citizenship requirements should be easy.
This assumes the filer wants French citizenship, obviously: if they want to stick with permanent residence but still want to vote then there's no solution, you can't have it both ways.
In the UK any resident can vote in municipal elections - there is no citizenship requirement.
Of course that's a bit beside the point in the case though. I guess that option is only open to EU citizens. I find that odd, but I guess that's the law.
I, as a US citizen living in Ireland can vote in local council elections.
- omg! so unfair
There are many stupid things regarding Brexit (primarily, that it took place at all) but this was a worthwhile thing to try to resolve even if it was a bit of a long shot.
I don't really think that should be relevant to France's laws. Britain could after all change their laws.
But I do think this woman should be able to vote in these local elections as a legal resident. That should be the case regardless of citizenship. But it seems that would require changes to French law.