Set the scene:
Beta (via Focus): Aloy, I need help!
(Aloy rushes over to see Beta hiding behind some debris with small machines all around. Aloy takes them out easily and helps Beta up.)
Aloy: What were you doing out here?
Beta: I was looking for a part I need for an experiment.
Aloy: Well, if you are going to be out here, you gotta learn how to defend yourself. (Hands Beta a bow and her old spear.)
Personally I would love to see Beta take a more active role in the series. A nice training session can be a great display of sisterly bonds. Plus, it opens the door for Beta to have a badass moment in the game, maybe even save Aloy's life someday.