She can't figure out what he's doing while all of this is going on, because the truth -- either diddling a child or watching mutely as it happens -- are both so out of the realm of possibility. "Playing Brickbreaker on your phone? Do I need to get the security cameras fixed? Because that's a $2500 bill we cannot afford. Do me a favor while I take the kids to school: Grow a pair." Which again, I think my only real desire to love Kash comes out of my inordinate respect for the way Ian does things, which made Linda come off a bit more harshly in my head than maybe she really did here, or was meant to.
Or maybe all these people are just assholes, which is what the show keeps suggesting but which I cannot accept. Because except for possibly Frank Gallagher, I can't generally buy into the "just an asshole" theory of people. It's not how it works in real life and it certainly doesn't work for fiction, because if that were true all stories would be six words long. For Sale: Some asshole, never learned.
(Plus, they snuck a previously into the Previouslies which still makes no sense out of context, where Ian is wearing a bathrobe and yelling at Kash, "I'm gay, not queer!" which could mean a lot of things but has almost certainly never been on the show, which means there's a scene we didn't get to see that probably adds even more background.)
The idea about potty-training Liam is that they'll save so much on diapers they can buy him awesome things like candy and small cars. "Ah, rewards for shitting," Steve grins. "The good old days." Fiona hands Liam and the potty chair over with a too-real "When Liam starts holding his breath and squinting, put him on this." Steve tries to pass her money for the electric bill, with the worst possible excuse -- "I'm almost living here!" -- guaranteed to get her hackles up, and we learn that the "I forgot to pay" thing was absolutely true.
"Lip's a bit flush this month," is something that Americans might say, sure, and we exposit about how it's SAT season and he's always got money from taking people's tests for them. Debbie says Fiona can't have the phone today -- "I need it. Cold-calling for baby-sitting gigs. I sound more mature on the phone" -- but Fiona takes it anyway and Steve drives the kids to school. On his way out the door, Carl hands over an urgent message from the school that is now five days old, of course, and scoots before they read it. She takes the Killing Bat away and then gets very stern with Steve about how she will not be having the money conversation with him again, because basically it strikes at the very heart of who she is to ever accept help in that form when there are still so many schemes and tricks up her sleeves that don't involve gifts from Steve. It ends badly.