I know,I said I need to be nicer...

This morning I was brushing my teeth.
She came right down the hall, shouting my name, while I was shouting back "ughblaeeeeth!"

If I sit indoors, she shouts "I'm just going to sit out here!"
Yep, ok.
"I saw that bloke today and he said he hasn't seen so-and- so..."
Oh.
"Hang on, I'll just come in and tell you"
Sigh.

It would drive me mad, too. But I don’t know what the solution is.

Perhaps develop a food allergy so that none of the food she brings is edible, borrow a large dog from someone - or what about one of those recordings of a barking dog that will play when she rings the bell? Or a baseball bat?

No wonder she's driving you mad, it would be my worst nightmare.

Oh wow, that's a lot...

I don't know what to advise other than, telling her straight, too may visits are exhausting you.

This doesn't seem healthy behaviour on her part and I'm not sure she will listen

It is.
Doing that would mean being stuck in my flat with the door shut, and hiding away.

20 years I've had this; well, "only" about 17 I suppose, because she was very much her own person when she first moved in.

How about just not answering and if she catches you later and says we’re you in you could say I don’t answer the door when I’m tired, I was having a nap. Or perhaps a sign in the window saying Do not disturb. A very difficult situation.