She might be shocked at first. Given that in the original story Morgana has her own complex relationship with magic, seeing Merlin's magic could stir a mix of emotions in her, like envy or a sense of relief that she's not alone in her magical abilities.
One possibility is that Merlin's revelation of his magic could lead to a change in his relationships. For example, his friends who were previously unaware might react with shock, some with fear and some with acceptance. His enemies, on the other hand, would likely see him as an even greater threat and might plot more vigorously against him.
Uther might initially be shocked. He has always been so against magic, so he could be furious at first. He might feel betrayed by Merlin, whom he has known for a while.
The storyline might progress with a lot of drama. People's reactions would be the key factor. If he reveals it to Arthur, for instance, Arthur's response could either make their friendship stronger or break it apart. This would then lead to different paths for Merlin, either having to hide again or standing up against all odds.
A fanfiction could focus on the relationship between Mordred and Morgana. It could explore how Mordred came to be so loyal to Morgana in the first place. Was it out of fear, admiration, or something else? And how does Merlin fit into this complex dynamic? He might be seen as an outsider trying to break their bond.
In some fanfictions, Prince Merlin (assuming he has some sort of princely status in this AU) and Morgana might be forced into an alliance against a common enemy. Maybe an ancient evil that threatens Camelot in a way that neither of them can face alone. They would have to put aside their differences and work together, which could lead to a slow - burning romance.
She could be shocked at first. After all, Merlin has been hiding his magic for so long. Maybe she feels a sense of betrayal initially, but then she might see an opportunity to have an ally in the world of magic.
Well, Arthur could feel betrayed at first. He has been brought up to believe that magic is bad, and here his closest friend has been hiding this big secret. However, as he realizes how Merlin has saved his life and the kingdom many times with his magic, he might come to accept it and even see the potential of magic being used for the good of Camelot. For example, Merlin's magic has defeated many enemies secretly, which Arthur might now understand as a necessary protection for the kingdom.
One great 'Merlin Morgana fanfiction' is 'The Bond Beyond Magic'. It delves deep into their complex relationship, exploring how their powers could have been used together in a more united way against the common threats in Camelot. It presents a unique take on their dynamic, showing that they could have been allies instead of adversaries.