It does happen way too often. Some parents in an attempt to find the best daycare for their child adopt a no stone left unturned philosophy and attempt to interview every daycare they can find in their radius. The result is someone as distracted as this parent.

I would probably simply reply with something to the effect of yes I know that finding the right daycare for your child is hard work and I know you only want the best for your child. Please call me next week if you would still like to set up an appointment to visit my daycare.

That way you are not telling them you don't want to see them, you aren't planning on a visit that likely won't happen and it gives the mom time to see everything else on her list so far and then only call you if she is actually interested in continuing to look at more daycares.