Also, Otaku-Dad makes an appearance. Have we seen Otaku-Mom yet? I can't remember.
She actually showed up all the way back in
ch4, pg21! Earlier than any other parent appearance!
So technically, yes, but not her face as of yet. Though as you can see Ijichi comments that mother and son look alike.
She may have had one or two other similarly brief and nondescript appearances since then, but if so I can't remember approximately where enough to track them down.