You can be absolutely sure, given Stef's physical problems, that Kiah would be getting a lot of "relief" minutes if Geno had any reason to believe that she would be an adequate substitute even for a portion of the game. The fact that she has basically been glued to the bench in the last three games says that Geno does not have confidence in her. As several people have commented, her major problem is at the offensive end, where she does not consistently post up aggressively, fight through the physical play by the defense and make herself available as an alternative on every possession. The offensive scheme requires the center to do that, and Stef (even with physical limitations) is doing it better than Kiah has demonstrated that she will.
Also, when Stef is off the court, Stewart is doing a very good job at all of this when she plays center, which gives Geno even less reason to consider playing Kiah.
