Lot of Sgt Jaxo fans (from the Trooper story) out there, myself included. It would've been great to have her as a companion, but certain...story choices you make would not have been possible (and thereby have meaning and enrich the story) if she were part of my crew.
This was the 1st person that came to mind after reading "wasted potential". But I agree they better serve a purpose as an NPC then a companion as much as it pains my troopers heart. I really liked a lot of female NPC's that could've been companions in my books.
The biggest companion potential wasted is still, in my books, Jaesa but that's a rant for another thread.