In a cameo perhaps, or more likely just a background pony. Since her 'reformation' there's not much to go on with regards to her character unless they introduce some new conflict based around her.
Why not all three?
We're speculating because we don't know. That's the whole point.
I'm surprised you didn't realize this but the irony of over-rating a character with such a large ego is really what's driven her appeal throughout the fandom, even if many fans aren't aware of the fact consciously. Her reformation in my opinion wasn't half-assed, it just bluntly showed that her character isn't really interested in being reformed because her underlying ego and self confidence is so strong that any humbling gesture is still, in her view, something worth appraising herself for. It's a sardonic smirk in the face of the show's sentimentality and high respect for its own message. A message Trixie may never really appreciate, at least not in how her appearances in the show have demonstrated(I haven't read all the comics though).
But she's likely never to come back for a full appearance anyway. The show has changed greatly since her last big appearance and I'm finding it hard to see how she would fit in.