I agree with the unlikelihood of them making two American Indian friend dolls- thought it would be an unprecedented move. My guess is that Kaya is still marketed aggressively, despite low sales, because of the respect for her character.

Singing Bird in particular would have clothes almost identical to Kaya, save for differences of a few embellishments. Mariana's clothes would be very different, but I still doubt their production.

As to Emily's looks being similar to Nellie's and Kit's- again, there is a precedent set for overhauling a doll's appearance. I wouldn't be surprised if Emily appeared looking markedly different than she does now.