I would totally send her a polite email saying you understand her decision to go with a half day program, BUT defending your day home, and your program, and tell her that you're sorry that you didn't get to tell her all that you offer in your brief interview with her. I do not think that this is a strange thing to do, given the accusation.
I couldn't and wouldn't let that go...
I agree with the idea of the follow up e-mail. And then end by wishing her all the best.
Always ensure that your child receives quality care by taking the time to investigate the provider and by asking for references! We simply cannot verify the claims of every daycare provider.
Updates
We expect providers to keep their listing and available openings up-to-date. However, to prevent oversights, openings expire after 45 days.