I noticed that On Demand has the entire season, so I FFWDed through the whole season, just watching the Jill/Aimee scenes to see if I missed something. First, there wasn’t much. Watching every one of their scenes for the whole season took less than an hour total, so it’s possible I may have FFWDed past one. Here’s the results of my pointless detective work:
In the first episode, Aimee thanks Kevin for letting her “crash their family dinner.” This wouldn’t really make sense if she were living there, so my conclusion is that she did not live there when the season started.
The second episode is when the kids follow Nora around, when Aimee snags some hand cream from her car. No clues to where Aimee lives, and then the third episode is all Matt all the time as he tries to hold onto his church and fails.
The fourth episode is Christmas, with the baby Jesus being stolen. This is the first time Kevin seems to acknowledge Aimee’s presence, where he fights with Jill (accusing Jill of stealing the baby Jesus), Jill storms off, and Aimee stays sitting on the couch eating a sandwich. Kevin gives her a snotty “Enjoying my sandwich?” that she doesn’t reply to. My best guess is that Aimee moves in right around this episode, either right before or right after. (EDIT: I’m pretty sure this is also the episode where Kevin dreams of a scantily-clad Aimee, who takes him to the woods to talk to the dog shooter guy.)
The fifth episode Aimee is there in the morning – in lingerie of course – so she clearly spent the night. When Kevin goes to Jill’s school to let her know that a GR member was stoned to death, as he leaves he tells her he left money so she and Aimee can order a pizza for dinner that night. So Aimee appears to be fully moved in at this point.
Sixth is all Nora all the time. Seventh episode we see Aimee “come home” from work to the Garveys, which helps explain why she was absent from so many house scenes in the fifth episode.
The eighth episode is Aimee’s last, the one where Jill accuses her of fucking Kevin. (“…on a pile of guns…”) Earlier in the episode, Aimee is at the family dinner with Kevin’s new girlfriend, Nora. Aimee asks Nora about her job, and if anyone ever freaks out. Nora wonders what she means, and Aimee says that “If I lost somebody on the 14th, and then had to answer a bunch of personal questions to get a benefits check, I’d go crazy.” This seems to strongly imply that Aimee didn’t lose anybody on the 14th.
My best guess is that Aimee’s father was long gone (daddy issues, fueling Jill’s accusation), her single mother joined the GR around Christmas, and since she was now all alone Jill invited her to crash at the Garveys’. Whatever the explanation, I find it really cool that even though Aimee moved in with the Garveys during the season, they never explained when or why, and then made her living situation a plot point when she moved back out.
It’s a subtle reinforcement of the “we’re not explaining anything” theme they have going on. (EDIT: Unless, of course, I missed a scene where they explain it.)