That’s a hard question! I am definitely not an expert in gender studies so I won’t be able to answer this question as well as other people would, but hopefully someone else will add a more correct analysis.
Also, I am not sure if you meant the relationship between Guinevere and Morgana or simply a ‘Morgana and Guinevere’, so I am going with the relationship!
I think novels and books managed to keep them apart more than together, even if in the Lancelot-Grail Morgana was one of the ladies at the castle and she interacted with Guinevere. So we actually start with texts that don’t see them interacting, but then we only have few interactions where Guinevere is just a collateral of Morgana trying to kill/dethrone Arthur, which is also in many modern novels. There’s also the problem of Morgana being picked as the main villain in media, which makes it hard for the narrative to let her have a positive relationship with Guinevere or even a neutral representation if the PoV of the book is on Arthur’s side or if the story simply the characters into good/bad.
In my opinion, I think that a good novel or media with good characters should not risk falling into the dichotomy trap.
Sometimes it’s quite disturbing to see Morgana and Gunevere in movies, as one is always extremely sexualized (leather outfit, lipstick, seductive) and the other is the opposite, or simply having Guinevere as the only positive character and all the other female characters (or the majority) end up being negative examples- I have a few books like that. Putting female characters one against the other, bashing them to be able to support one and not the other is basically one of the reasons why I didn’t like The Mists of Avalon, which I still recognize as the first important arthurian novel with female protagonists.
I still think the main problem is how female characters are cut and while we have all the knights and Arthur and Merlin, we often end up with just Guinevere and Morgana in media, as representation of the good and the bad, which makes it annoying because the other female characters are often rare.
SORRY. This answer was terribly long and confused.