I'm pretty sure it was Mariyanuu. I remember seeing information about that somewhere.
Looks like no one was 'added' as such, what info I could find had both Team A and Team K with 17 members O.o When Shihori left they moved Mariyannu from Team A to B, and the lady whose name escapes me, but was originally in B, was moved to K before finally moving off to SDN48 left as well, making all the teams 16.