One of my favorite books (The Gift of Fear, by de Becker) talks about how to end relationships with stalkers. (I would consider this stalking.)

He says, basically, to just end it. Don't talk about ending it. Don't talk to them period... since any contact you have with them (even if it's negative) reinforces the connection and obligation in their eyes.

Just end it... don't allow her in your house. Don't take her calls, or end them immediately.

Also, try to figure out if she makes you feel "special" in any way... if there is anything YOU are getting out of her acting this way that may be keeping you from calling a halt to it. (For instance, does it feel nice to be paid so much attention to, esp by a person you describe as sweet and good hearted?)

When I wanted to end it with a neighbor who was intrusive and harassing me I just refused to respond to her... she visited, called, asked what was wrong. I just always said "nothing" "I'm busy" "I can't visit now" etc.

Eventually she got the message.

Good luck.