Haven't done that one in a while, but the way I remember it is once she gets the weed, she'll remain in the house doing nothing as you said, but will show up in a cutscene that triggers somewhere in 7th street when you go there.
Edit: happened upon another recently made topic about this which said that your time has to be something early morning like 6 - 7, for god knows what reason.
Since one of the member babies is the request, I'll need like 20 minutes to create it. Will also supply the nature and ability of choice. I assume you're able to access the room where it becomes Magnezone?
Or Rhampardos / skull fossil. I've got some form of everything else in the game, so I can offer either A: Anything, but its stats would be whatever they happen to be, Or B: To make a baby of one of my actual team members, which would have all 29 - 31 in the stats that matter. Those are Greninja, Torterra, Magnezone, Crobat, Chandelure, and Klefki.
I can do Oshawott for a chimchar, or cranidos / rhampardos / skull fossil. Chim seems to be the only starter left that was never anywhere else, and I found my entry for cranidos to be empty after having already double mined every rock in the game. Btw, an NPC inside a house in Agate traded me a Litten for a Stantler.