Let's put it this way: I'd sooner be alone with a sheep than be alone with Penny. She's the type of person who looks as though she's whispering when she talks. Just the way she carries herself makes you think that she's telling you something you ought to feel guilty about hearing. I would never say anything to Penny that I didn't want to have come back at me. She's simply not to be trusted. Certainly her most redeeming quality is Stephen. And how much does that really say?
When we first meet Penny, we have every reason to believe she's not a likeable character. After all, Jean doesn't hunker down and try to hide from anyone else that we know of. Penny doesn't even take care to remember Lionel's name. And when she's corrected, she forgets it within minutes. She's busy listening to herself talk. She's loud, gossipy, and thoughtless. She belittles her husband every chance she gets and she gets lots of chances during the run of this series. What's more, she seems to have no idea that she is as offensive as she is. She's the type of woman no-one wants to be left alone with.
Jean does her best to justify Penny's demeanor, reasoning that she means well. The closest anyone in this series gets to telling Penny the real truth is when Stephen tells her he doesn't want to have her work in his office because she's too nosy. As Lionel says, he's "heard of people hanging themselves, but Stephen actually builds his own gallows." Everyone else seems to be just satisfied with a roll of the eyes, which is perceived by everyone in the room except Penny. She wants to know the latest dirt on anyone and she doesn't limit that to family. Sandy or Judith -- it makes no difference to her. For every action, there is an equal and opposite reaction, I'm told. Well for every compliment Penny gives, there is an equal and opposite insult. She never seems to say things without attaching a "but," and everyone who interacts with her is alert and waiting for that "but," to drop.