What part of "human is her altmode" are you not undetstanding? Sari's two modes are human and robot. Sari is a humanformer. Sari scanned Sumdac as a protoform and took on human as her altmode. Sari transforms from human to robot and back.
Why do you accept Blackarachnia and Waspinator as a spiderformer and waspformer, but not Sari as a humanformer? Why do you accept Optimus Primal as a gorillaformer, but not Sari as a humanformer?
Sari was the first humanformer, but she hasn't been the last. We've four more since her, and that's not even counting Sari's evil alternate universe self.