I would relax. I understand your apprehension, but the fact that you're full and have never had to advertise, to me, means you're doing everything right, and will continue to be full.

My neighbour in our new house is a daycare provider too. I was upset at first, but now I look at is as possibly advantageous - maybe we can trade off sick care if neither of us are full...etc.

I don't think it's a big deal if she even copies your contract, as if parents are interviewing more than one provider, you will present a united front on all the points in your contract if she's using the same one as you.