Hmmm, I think the poor mental capacity to deal with immortality is barking up the right tree. You might start out fine but can you picture the long term effects? Soon enough you would have seen almost everything there is to see in a city, done almost everything, nothing would be exciting anymore. Soon you would likely start seeking greater and greater risks in order to feel something other than boredom, in time as friends or family start dying and your left alone with other immortals your life would become more empty and hollow, even the fires of hate become ashes given time. You may even come to view immortality as a curse, one that you inflicted on others. Would that sit right with you, forever? In the end you would likely be suicidal or at best apathetic about everything, even frienships wane over time.
Maybe end it with her, alone, in the future a solitary figure likely half mad and seeking a release, she got her victory, after so many long years, only to find it empty and hollow, she just destroyed the only thing left that gave her purpose?
Queue a new, deranged villain, the very person originally fighting them?
Or maybe she has the courage to end herself or wipe her memory totally so she can find the world new again, with a different innocent and naieve version of her at the helm, ready to repeat the same never ending cycle anew?
Excuse format im typing from a ps4, laptops battery is fried.