In the 1990s I read a sci-fi novel, a one-off book (not a series). It began describing a futuristic time where people either have brain-augmentation or senior citizens have the option to discard their human body for a brain-box (the human brain is placed within a "box") to continue existing & interacting with the outside world. Maybe both augmentation AND brain-box were included in the story??
Anyhow, after the brain of "Ger" re-connects she starts to interact with her offspring (a teenager I think or a young adult, possibly a gal or e-fem male).
I only remember that the teenager/young adult has a huge adventure trying to escape their fate AND not lose contact with Ger's box (brain-box) AND hold their allies together as a search for the father is conducted.
I believe that the father has connections with a political figure (female??)... who bore a step-sister (is 8-12 yrs now)?
In the end the political figure (step-mother??) of the teenager/young adult is confronted. A duel to the death is ensues, yet one of the teenager's allies becomes champion-of the teenager/young adult... winning the fight, and succumbing to lethal wounds.
The rich step-sister becomes an ally of the teenager/young adult.