Sorry it took so long to answer your question. Feel free to ask all you want and I will try to respond.
Since you don't know when she went broody it may be hard to know when she should quit. They are usually pretty persistent about staying with their eggs. If you are sure there are no male guineas in your neighborhood then it might be best to go ahead and break up the nest. If she is in an unprotected spot she is vulnerable to any predators that may wander by.
On the other hand, if there are males around then it's possible she may have fertile eggs. It takes 28 days for the babies to hatch. When you are sure she has been on the nest longer than a month then just chase her off the nest and destroy the eggs.
Let us know what happens.
The only other thing I would recommend is to have food and water where she can find it without having to be gone from the nest too long. Just don't put food too close to her nest because that could draw in a predator.
A mile away may be a little far for most guineas to travel for breeding. But you never know with ones that have become wild. She evidently came from a flock somewhere and she might know how to get back there to be bred. But for some reason she has made your place her home.
If she hasn't added any new eggs to the pile in the last week then she is full on broody. All we can do now is wait.