Was the kid's mother ever shown on the show?

no. she was a character that was always talked about, but never seen.

Bernie actually showed an old photo of the family.
at the Christmas episode.
but you can't see anything.
one of those old Hollywood pics doctored up.
neesie plays his other sister.
but no, his sister, living and breathing is never on the show.

I wondered about that too because I was watching the very first episode today and they were talking about her going into rehab and Bernie was speaking to her over the phone, but she was never shown.