I don't know if is just me but since Sara is dating Oliver she does not hang out with the other girls as they used to. For me all those "problems" of Sara getting apart of the other girls (specially of Taylor) started since she is dating him. Tell me if I wrong
I think that something happened between Sara and Taylor for sure. But with Martha and Stella, well I never saw that they were close and maybe she just congratulated them on private or something. Who knows