A part of my novel will take place in the future. There is a group of people who is convinced that they are the last generation of human beings, that the human race would be better of extinct, that everyone born after a certain year is "not meant to be" and all that. My MC is obviously one of the many who were born after that particular year.

The MC has a low self-image, she thinks she screws up at everything she does. One day her brother-in-law gets killed whilst fighting one person of the sect described above and the MC wants to prove others and herself that she is in fact not entirely useless by travelling back in time to save the life of her brother-in-law. Only then she is unintentionally responsible for her brother-in-law's death and realises that she can't change the past. MC feels miserable and is ashamed of herself and travels further back in time to live in a complete different time period so she can avoid everyone she once knew.

So where I need help:
A few years after the event, MC's nephew is all grown up and is sent out to bring his aunt back to her original time. I need a good reason why she would be needed back but I don't want that reason to be 'because her family and friends miss her so'. I'd preferably want it to have a connection with the sect listed above. I want her to be seen as useful and I want to give her the opportunity to make her feel more confident about herself.