itch.io

If you're talking about what i think you're talking about, you have to pick the mushrooms in a field that you can find by Exploring the Outskirts. It's been a while so I'm saying this purely from memory but I think you find them at South -> South -> South maybe? 

Either way, that field is where you get the option to pick mushrooms and bringing the correct one back to her will let you move on to the lessons iirc.