Does Amanda actually just... give up searching for her mother and die of old age? Does she get killed and there's some kind of corporate cover-up?
She won't have been killed. Ripley recognized her in the photograph in the movie, and (If I remember correctly) in the audio drama for Out of the Shadows, Ash learns that she worked for WY, survived classified events and then got married back on earth.
While the ending to Isolation may be somewhat vague and mysterious, it appears she was picked up and likely survived a debrief by the company and then went on to live her life.
But if you ask me, that whole business of an Alien being onboard the Torrens was a nightmare.
What I think really happened there is that she was knocked unconscious when she blasted herself and those Aliens loose from Sevastopol, because (if I remember correctly) she hit something at speed. I sincerely doubt she'd even have had enough oxygen left in her suit (at that point) to escape the Torrens, calm down and go to sleep in space, let alone drift for Lord knows how long.
The light that shines across he face at the end is likely the Torrens, which picked her up within minutes of being knocked unconscious, and transported her safely home. Verlaine would be in a position to help her confirm any story, thus allowing her to leave the company and move on with her life.