Commence cardboard box maneuver!
If Sawatari Makoto has a bone to pick with you, no statute of limitations applies. She is completely willing to strike in broad daylight with no warning whatsoever. That she doesn't forget her grudges doesn't mean she remembers the reasons behind them. The sight of your face made me really angry works as explanation enough for her.
Her anger will dwindle sooner or later, though, and Makoto will grow attached to you. Care to take in a poor and homeless redhead? Makoto has no place to return to and no memories of who she is. When you see her serene sleeping face, you might even forget about her usual trickster ways.
There is a deep-rooted conflict within this bright girl. She doesn't trust others, but fears being left alone. She loves pranks and the attention they bring her, but doesn't want to disappoint those that take care of her. She declares her dislike of the people around her, while secretly doing her best to keep them around.
The mysteries surrounding Makoto will not be easy to explore, and it might turn out there is not much time. If Makoto came from nowhere, where will she leave for when it's time to say goodbye?