Bumping this thread because we're still lacking proper act 3 Minthara, despite 3 major patches
I don't think that content ever existed. Minthara is like the other non-origin characters, her stuff is limited compared to theirs. There might be some dialogues that don't trigger but thats about it.
The Act 3 Minthara overhaul you are looking for wont be in until a year from now... maybe two. That is assuming Larian would even bother with such a project. Which I really hope day will, I think Minthara should be available for a good playthrough and she along with ALL the other companions should have more scenes in Act 3.