Oy, I had a coworker who was like this. Asked the most wildly inappropriate questions. And the most important thing I learned is that you NEVER give her information. It's like a drug. Once she gets a little bit, she'll never, ever leave you alone. Every little bit of info she squeezes out of you just gives her more questions to ask. Don't ever think that it's impolite not to answer her questions, I had soft hearted coworkers that felt sorry for her and would get sucked into a conversation, and before you know it she's grilling them about their 'relations' with their spouse (really

).
People like this are actually pretty easy to handle. It takes a combination of breezy cheerfulness, selective deafness, and distraction.
If you're outside picking up the mail and she starts heading your way, smile, wave, "Hi, Mary!!", and walk briskly into the house. You don't need to stop to talk to her.
If she does manage to corner you, and asks a barrage of questions, start talking about something else. "Oh, my, look at that beautiful tree. Do you know what kind of tree that is?" If she asks some hideously nosy question, pretend you didn't hear it. Talk about the weather. Compliment her on her blouse, or her hairdo, or whatever. If she asks "How much money does your husband make?" You say, "Oh, Mary, that's a lovely dress, it's such a good color for you!" Selective deafness, followed by distraction. Just long enough to be polite, then you're out of there with something like "oh, my, I have to start my cleaning, I have a busy day today. Bye!"
It's possible to smile and be polite and cheerful, and not give her a bit of information. Keep things as superficial as possible. That way your relationship stays non-confrontational and she can't say you're mean or unfriendly.