She didn't expect Shamiko to find a magical girl, barrier prevents it.
Seiko is out of the loop on magical stuff, Joshua was the one with underworld connections
Seiko wasn't even told the Dark Office shut down. As soon as her one outlet to the magical world, Joshua and Sakura, died, Seiko is entirely disconnected from magical things, she's basically swimming blind here. She doesn't even know if all the other magical creatures are still alive out there, all of her connections are lost, magical girls could be coming any day to kill her family and she'd never know it.
But there's meaning in getting Shamiko introduced to the family bussiness and teaching her to act like a demon after awakening, even if she doesn't go and fight magical girls for real.
Shamiko is all concerned about being a demon when she grows horns one day. Seiko gave her a clear objective, and helped her along. Taught her about her culture and her family, which Shamiko tried her hardest to live up to. Shamiko transitioned to being a proper demon properly because of Seiko's guidance.