Morgana would not give up this cause, no her birthright, without one hell of a fight, She'd lost far too much as it is, she'd lost her mother when she was not even 5, leaving her with a father who was hardly ever home (seeing as he'd been away fighting Uther's wars) When Gorlois died, she was only 10. Within a month of his death, she was packed away to Camelot, where by the time she was 15, she'd fallen in love with the Prince, she had loved him with all of her heart, and Arthur had taken her love, cherished it, let it grow unchecked, and then...crushed it like a child does a bug, he left her broken for two servants, and she'd never forgive him for that.
She had loved Uther (as much as she hated him) and it made her heart ache to hear of his death.
She had lost Morgause, not even had her truly, Morgause was...well Morgause was Morgause, She reminded Morgana of Arthur if she truly thought of it (at least mildly in appearence if nothing else) and had spent twice as many nights in Morgause's bed with just the silk sheets covering them than she ever had Arthur. She may even have loved Morgause more than Arthur (no she was deluding herself there)
Merlin had betrayed her so many times, and she only now knew how far his betrayal went. He had claimed to be her friend, had tried to help her. and all the while, he wasn't honest at all, everything he said was a lie. and she couldn't decide if it was better to know this or worse.
She'd lost Gwen more than once, once to Arthur & his new found love, second, to Arthur curing her from Morgana's enchantments. She had simply wanted her friend back, and Arthur took her once more.
Mordred may be the betrayal that hurt the most, she had treated him, cherished him, as her own. and he'd stabbed her for Arthur (he always seems to win doesn't he?) She couldn't even define the love she held for Mordred, and he'd stamped it down until it was dust (which her heart was now wasn't it?)
She would not give up this fight, she didn't care that Arthur had been stabbed, she was going to make sure he suffered before he died, so he knew...KNEW that, if she couldn't have Camelot, her true Queenship (Birthright or marriage, she deserved it!) Arthur (her true love) than no-one could. if she died in this process, she would die a true witch a TRUE Queen, who held onto what she believed after what she wanted, and no-one could stop her. She would get her final revenge, and Emrys(merlinservantfriendyourlover s-noyourbrotherslovernow, her mind kept whispering) wouldn't even be able to stop her.