slayer747, I think that's the second season if the wedding hasn't happened yet. I think the wedding is the end of the second season (or it happens after planning it at the end of the season--I haven't seen any of that yet--but I think they are already married when season 3 starts). The first episode of the third season (301 "Busted") has: "While Rick, Lily, and the kids struggle to live under one roof, Eli is arrested for marijuana possession." (and some other stuff that sounded too spoilery for a pre-viewing description)
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They list Mischa Barton (Katie) in episodes:
308 "The Sex Show"
309 "Tough Love"
312 "Gardenia"
313 "Falling In Place"
314 "The Gay-Straight Alliance" (***Do not miss***)
317 "Experience Is The Teacher"
318 "Losing You" (only a very short appearance?)
319 "Chance of a Lifetime"
To make sure you're on track, the baby shower is in episode 306; and 307 sounds like a Thanksgiving episode.