I agree with Avirah that CS is fooling herself. Not that she considers herself a tzaddekes or a beinnonis, but that she has had “beinoni moments” and that she feels the joy or her neshamah or something along those lines.
It is so easy for the yetzer hara to fool someone into thinking that an action, speech or thought they did/had was good, and we should never consider ourselves on the level where we feel satisfied.
When the Tanya writes that a person should consider himself a beinoni I believe he wasn’t referring to every Tom, Dick or Harry (or their feminine equivalents). He was explicitly referring to the maamar Chazal that if the whole world says you’re a tzaddik you should consider yourself a rasha, and on that he says even if you are free of sin consider yourself only a beinoni.