Board Thread:Character Discussion/@comment-26715865-20151130090817/@comment-1894786-20151201020604

Bex has stated multiple times that she took from Mary Poppins whenever she's being sickly sweet (it's most noticeable in her midwife guise, which is the only time Bex directly mentioned it as being Mary Poppins-ish).

So yeah, Zelena is Mary.