It is reasonable to conclude that Minthara would have less content than other, more visible characters, because they are available right from the beginning of the story. We know she's an optional character resulting from the "evil" Act 1 path...but it's a matter of degrees.
Right now, we're not even sure about whether we've seen all the MInthara content or if there are bugs or glitches involved preventing us from finding more conversations with her that are relevant for players who chose to have a relationship with her.
Otherwise, it seems you can invest a lot in making her join your party and only get a partial reward for that.
