I do understand the lingering feeling of first love.I also had one and it's really difficult for me to move on even if the other person is very toxic.But what doesn't feel right is the way she is too careless.She doesn't behave like an adult, it's like she just acquired a premonition from the future and not experiencing it herself.I think it's better for her to really plan out and predict the cause of the accident(the accident of the first love and herself with the black-haired guy) since she knew the rundown and that is one of her advantages of time travel.I hope this story goes well.
P.S. I think this movie will be one of the pivotal points of the first love's accident and she caused it herself