My guess Larian have intended for Minthara to be at least a camp companion, if not party, to balance out that a good playthrough would have Halsin as camp companion (and also Jaheira and Minsc). But the the entire main story got changed to make room for the emperor late in development, and I think they did not bother with the evil path because it was less popular. So now they try to patch her to fit into a good playthrough instead, but they don't playtest content properly before releasing the patch.
