Your cat may also be responding to a territorial cat outside your home that is making her nervous.
and also that paragraph about stress:

it's entirely possible that this started when we got our dog mussie. He is ah. . . very friendly and loves to um, play, with our cats.

the only time my cat gets vocal is if i stop petting her xD

or maybe it was teh box getting too dirty. Mom usually takes care of that so i've never looked for myself