This made me go hmmmmmm. After all, this is a story that probably has most of its roots set around 450-550ADish, in a period that is almost completely undocumented, for which even the archaeology is confused and confusing.
The written sources for those confused roots are from documents from almost 400 years later. And then, they provide no story that is in any way recognisable as the 'Arthurian story' as people think of it today - and they don't mention Morgana, who may be in origin a goddess or a spirit rather than a historical person anyway.
Should Morgana be wearing shoes from 500AD? From 450? From 550? Should she be wearing shoes from Somerset, or shoes from Newcastle, or shoes from Brittany?
Maybe she should be wearing shoes from the twelfth century, because of Geoffrey of Monmouth, or whatever kind of shoes the Welsh goddess Modron wore - assuming we can find an appropriate archaeological or artistic reference for early British Goddess-shoes?
Maybe, she should be wearing shoes from the first century BC, because in the French romances she has a liaison with Julius Caesar, or thirteenth century shoes, because that's when those romances were written, and so those shoes are probably what the writers would have visualised her wearing?
Or maybe her shoes should be from the fifteenth century, because Malory's version of the story is quite close to the one that is most familiar to us? Or perhaps nineteenth century shoes would be best, to fit in with Walter Scott and Tennyson?
So far as I can see, we have a range of Possible Appropriate Shoes for Morgana that ranges well over a thousand years, and you could reasonably argue for two thousand.
Morgana is not a person from history, so I'm not sure why her shoes would be from history either. The Arthurian legends are not history. They have no 'authentic' time when they are set. They are self-contradictory accretions of story that sprawl across so many centuries that almost nothing is consistent - not even the identity of the king, or of his enemies. Mocking the inauthenticity of the shoes is a drop in the ocean when the entire story and all the people in it are inauthentic to any time period more specific than Yore.
The story and the characters are fantasy, not historical fiction. The presence of griffons and the ability to cure everything with a decoction of comfrey may hint in this direction.
As I see it, there is this odd idea that history is history, and fantasy is fantasy, and anything before Tolkien must be history. But of course Tolkien didn't invent fantasy. Fantasy is just what history used to be, before it decided to cut its hair and get a job. I am undecided whether fantasy is nowadays history that has decided not to sell out, or if it is just history's weird hippy uncle that wanders around smoking odd things.