I decided to give a few of my ocs pokemon teams for fun! Here's Serpentine's team:

Ekans- She already has a purple and yellow snake companion so this was a perfect fit! In this universe I think the ekans would be Serpentin's starter pokemon, instead of finding it after Serpentine goes on the run.

Shiny Galarian Yamask - A large part of the mystery surrounding her friend's deaths has to do with an ancient ruin and the artifacts that were left behind by that civilization. So the ghost typing and general back ground are a perfect match! I imagine oce she gets closer to the answers she's looking for it will evolve into runerigus. Also I think the shiny fits in with her color scheme better. She would have found this pokemon at the same time her friends died.

Unknown (s) - For a similar reason as the last pokemon, this solidifies the connection Serpentine has to the ancient ruin.

Lucario - I wanted a pokemon to represent her time in Gael's fighting ring, and I think Lucario is a perfect fit.

Not really sure how balanced this team would be in a competitive sense, so feel free to suggest pokemon or types you think might make her team more well rounded!