Didn't think of it that way, it also makes a lot more sense than my theory. I just have a feeling she's involved.
I'm really hoping it's just added bits of dialogue to get people thinking and cover up other events that have been foreshadowed. I really, really don't like the idea of things with Katie turning sour but, like you say, a few things mentioned do point in that direction.
I do agree, the theme is trying to do better than those that came before so it could be that it is set up to do that and they work through their issues to then finish off whatever is set up as the big bad.
The mother being involved somehow would make sense as she gets mentioned just a little bit TOO much for her to be a throwaway character. But at the same time given she needed to do what she did in order for her Coven or whatever they are called to disband in order for Sorcery to bleed into the human bloodline so being talked about makes sense. Hard to try and guess where Droid is going with it. Any plotline around her puts Chloe front and centre so it could be a nice easy way of expanding her character and giving her more screen time.
If we're following the usual tropes, Katie can go two ways. She becomes an issue, or she deals with it. Becoming an issue is bad for basically all concerned because it's very plainly laid out the MC won't leave Emily so unless we get a bit of Merlin magic and an Evoker can become a chosen, she's very much on the outside looking in. It's also bad from a players perspective as she's a great character and a much loved one, so having her turn bad or at the very least cause friction will be a bit off putting.
She can deal with it by being happy with what she's got, accept the relationship she has with the MC. Which is also a problem as it's basically hinted that's not how her family role. Fia's talk hammers home the idea this WILL become an issue and not one that can be fixed by giving her a bottle of booze.
I suppose there's a third option where she dies before it becomes an issue that needs to be dealt with. Clean from a story point of view but suffers from the same issue as her going bad in that the fans would be most upset. It does fix an issue missing from the game so far and that's the issue of loss. The stakes haven't really been hammered home yet of what's at stake. Mexico is gone but that's just numbers to be MC. Typically writers do this by killing someone close to the MC (Emily's da doesn't count). No way will Droid fridge Emily and the MC's unborn daughter (although that would be effective not to mention brutal as FUCK) and fucking with the chosen probably won't happen as it would turn the MC into a killing machine so it would have to be the second tier characters. Dylan, Chloe, Katie, Hakone (although would the MC be sad about that one?)