Billing is negotiable. Your agent would talk with the casting director about your billing, but generally, there’s featured (you have two – five lines), co-star (you’re in a whole scene or two) and guest star (you’re very famous and/or your part is integral to the episode and you have a lot of scenes).
The best case scenario for the guest actor is that she gets a separate card at the opening credits. That means her name is on the screen by itself at the beginning of the show after the regular cast is listed. Next would be a shared card (her name shares a screen with other performers) at the beginning of the show, and on down to being put in the end credits where only her mom will look for it. Extras, of course, get no billing whatsoever.