Seems to start appearing in Seasons 5 or 6.
She doesn't seem to be credited at all in:
http://www.imdb.com/title/tt0370194/fullcredits#cast
(No it's *not* Cathy Shim)

If you remember the scene where she explains to Clementine about longhand and shorthand jobs when taking memos.
I think her character is a clerk.