Someday, maybe after I retire or Bannerlord comes out, I'll get around to making the mod I want to make where she becomes the claimant for Aileach. I wanna copy and modify her seduction minigame conversation to be you persuading her that her uncle Aed is to blame not just Mael Bresail and that you and she could and should try to overthrow him. Outcomes of her ruling like a normal claimant, her marrying you (giving right to rule), her leaving (either cuz you're trying to use her to gain power, she decides she doesn't need you, she doesn't want any more war, or cuz you killed her brother and niece/nephew), or staying with you for a while as she considers things. Having the Cathach will help persuade her to fight, as it's God's will that she miraculously recovered it from the Viking who stole it.