You have to bring your mom/Aiko to her on the first sunday in-game, after 4 p.m. to the shrine near where you live.
After that she roams the streets mostly, but every sunday from 4pm onwards she's at the shrine where you can also always access the magic shop, whith or without Lily present.
To find roaming Lily you can click the little target thing on her "girl's status" page, right over her picture.
Later you can upgrade your abilities and teleport yourself to one girl or the other way around but at the start you have to do some walking.