The problem is that Minthata wasn't on the nautiloid. I think it would be a difficult job to fit her appearance in the existing framework. A lot more difficult than the other origins in any case.
Not any more difficult than making Durge work. Given there's no reason they should be on the nautiloid what with having being tadpoled a while before the rest of the cast.
Something simple like "The nautiloid picked up some loyal True Souls to aid in its defence" would be able to explain her presence on the nautiloid at the start of the game (Though wouldn't explain her being a level 1 pleb with no tadpole powers...)
The biggest snag would be... The entire rest of the game. Having to implement brand new lines to incorporate Minthara's interactions during Act 1, potential for a "Good Playthrough" interactions at the start of Act 2 and a bunch of altered and added lines for having a PC Minthara.
In short, a lot of work for a game that is no longer in active development.