Shannon's been hurting ever since we met her - she was in a toxic marriage (of which she was one of the two tangoers, I don't deny), and now she's in a divorce with a guy who has always struck me as emotionally inaccessible and prone to abusive hostility. She's at a low point among low points and is hurting and afraid. The complaint about the house isn't about the practical aspect of having to move, it's the frustration of the endless change, the inability to set roots, and the worry about whether she's falling short as a mother because she can't keep a consistent home.
Is she acting self-centered, sure, she's deep in her shit. But she's not a true narcissist; she just seems like it right now because she's in such pain. The difference is that she's capable of apologizing and has the capacity for introspection, qualities you won't find in a real narcissist (ahem, Vicki). The way to change the behavior of someone who's hurting like that isn't to yell at them. It's to listen compassionately. She needs to heal all this hurt with the help a good therapist and the company of kind people.
She chose the worst possible "friend" in Tamra. Tamra's the scorpion from the old fable, the one where the frog agrees (reluctantly) to give the scorpion a ride across a river. Halfway through, the scorpion stings the frog. As they're drowning, the frog asks why. The scorpion shrugs: "I'm a scorpion, it's what I do."