So why is she represented as a malevolent entity in the waiting room? Even Maddie warns "watch out for my cousin"
The cousin lines have double meanings. The very first time you se Laura, the Arm explains "She's my cousin -- but doesn't she look exactly like Laura Palmer?" The next episode, Laura's identical cousin Maddy appears. The line works to foreshadow that. But it also works to foreshadow that the waiting room or lodge is populated by doppelgängers, cousins of spirits like the Arm, who look exactly like people. Maddy's line "watch out for my cousin" can apply to Laura, or to her own doppelgänger, as it's delivered in the scene introducing doppelgängers.
Creamed corn? Ya wut now? Garmonbozia.
Garmonbozia is suffering as a physical substance. Creamed corn is how it's represented onscreen. There's no special meaning to the fact that it's creamed corn, they just needed a simple way to depict suffering as something you could eat or have stolen from you. In FWWM, blood is transmuted into garmonbozia.
Eerie monkey at the end of FWWM saying Judy?
Related to when Jeffries reappears in Philadelphia yelling "We're not gonna talk about Judy, in fact, we're gonna keep her out of it." This is a plotline that didn't get fully revealed o developed.
If you haven't watched it yet, watch The Missing Pieces before starting S3. It expands on FWWM. If you can't get a copy, at least watch these segments: