A pre-visit is never a good idea, @Thomas1517 , as you have outlined. That's what the photos, reviews, description and rules are for.
There are two lines you can use. The first is that it is not allowed by Airbnb. This is true, and I never mind blaming Airbnb for things I don't want to do. They have big shoulders. Find the policy and quote it.
The second is that you are fully booked. You are. You cannot have people traipsing through private areas being used by paying guests. I use that one quite a lot, too, but mostly when someone off the platform wishes a tour.
You do not have to let anyone in before the booking begins. If it gets tense, you can suggest they book somewhere, like a hotel, that perhaps allows tours. You can "understand completely" if that is their decision.
You didn't ask about this, but bookings from locals bring their own sets of worries, and more so, given that she is asking for the address so many weeks ahead. You might ask why she needs your place when she lives so close by.
