1) Join The Conspiracy
I feel like Cath was using Roderick as a pawn (probably has other guys wraped around her finger too) & may reach out to MC (letter, abduction ect...) in order to offer him a place in her conspiracy. This may line up with us being in charge of a bandit hideout while we help her topple the Baron. She could be the Baron's daughter or someone related to the late Duke who wants to take the power of the throne for herself. The bandits for her are just a means to an end. (Bandits or Cath or both may try to turn on her/them/eachother afterwards)
2) Working Both Sides
Perhaps you'll get a chance to work both sides. Until the game makes you choose to side with the Baron or with Cath (This is if Cath & the Baron's daughter are not the same person). If you side against Cath then she will be executed or perhaps imprisoned & Baron gives u a reward OR you side with Cath & she takes over. This could be an infiltration task by Cath to get the Baron's trust & the Baron starts give shit to the MC that will make players think "mabey Cath's the bad guy?" Creating the choice.
Honestly that sounds far to sterotypical and boring... let alone that the MC is a terrible actor and lier.
There is another Way this could go that sounds more interesting to me...
Cath attempts her takeover and fails.
All her men are either captured or dead, but the Bandits Roderic had gathered weren't involved in the take over (since he died long before that event)... Cath is on the run and seeks them out in order to employ them for her protection.
The Bandits act up and the Player deals with her as a Bandit Queen... You can get access to her without involving greater forces/powers or expanding this into a realm builder.
Maybe some soldiers hunt her and the MC uses his Goblins to get rid of them (like with those 3 knights) and than put her into his own dungeon