Sofia: "I believe your instincts. I don't want you to ever doubt yourself or your choices."
Mia: "Just everybody else."
Sofia: "There are plenty of people in the world who are for real. Maybe Kyle's one of them, sure. But caution is a skill best learned early. It doesn't mean you're bad, just smart."
Mia: "I have met a lot of people who wanted to be around me for the wrong reasons. I know what they look like. They look like my drug dealing clients. They look like their hair is made of carpet. And anyway, considering you were Dad's assistant before you hooked up I'm sure people made assumptions about you."
Sofia: "You bet your ass. But your Dad knew I was for real. And then you came along..."
It gets weird: "And anyone who couldn't see how much I loved you is not worth thinking about, are they?"
Which makes no sense in context, but adds a lot of texture to the red herring idea that Sofia would kill Vivian (or Samantha) to keep Mia (or the Tater Tots) close. It's a fairly on-the-nose way to keep her in the mix as a suspect -- childless second wife obsesses on the family's babies because her stepkids were all grown up by the time she arrived and mostly seem to hate her anyway -- but when you're constructing a parlor mystery like this it's enough to make sure that people with lamer motive, like Sofia, balance it out by being utterly fascinating.
Like c.f. Julian, who has the most motive out of anybody and no personality at all. Or Robert, who spent the first two episodes crying and being pants-shittingly scary by turns, but has never stopped talking about protecting the family no matter what. Or Edward, who is supposedly the most dangerous person -- and serves to question Joanna's presence, of course -- yet has negative motive for the murder itself, but whose backstory and portrayal make him wonderful:
Robert: "Edward! I was just going to invite you to the driving range..."
Edward: "Am I a murderer? Did I kill Kimberly Yaeger?"
Robert: "What a silly question!"
Edward: "Is it, though?"
Robert: "What on earth, Edward. Where's this coming from."
Edward: "Haverstock. He's threatening Lyritrol, so I visited him, and he told me I raped and strangled a girl."
Robert: "I wouldn't worry about it."
Edward: "Okay but Dad. Like, why not just answer the question?"