What is the origins of this antique fine china teapot and what is its worth?

It appears to be from the American Arts and Crafts Movement. 1890-1910. Americans were encouraged to create their own art. There were many schools and clubs where people could go to create art. There are many famous schools that are known to antique dealers. Pottery was especially fascinating to women. You didn't mention where your Grandma grew up. There might be a clue there. China is a hard medium to work with. There can't be that many schools that worked with it. You'll have to do some research in your area of the country. Or ask an antique dealer who is familiar with Arts and Crafts. Was she from Chicago by any chance?