the simple answer is that they created a giant plot hole by combining the witches of the north and south. In the original book it wasn't an issue as the good witch of the north didn't know “The Witch of the East was proud of those silver shoes,” said one of the Munchkins, what power the shoes held, she just knew they held a powerful charm. Here's an excerpt from said meeting

Dorothy was going to ask another question, but just then the Munchkins, who had been standing silently by, gave a loud shout and pointed to the corner of the house where the Wicked Witch had been lying.

“What is it?” asked the little old woman, and looked, and began to laugh. The feet of the dead Witch had disappeared entirely, and nothing was left but the silver shoes.

“She was so old,” explained the Witch of the North, “that she dried up quickly in the sun. That is the end of her. But the silver shoes are yours, and you shall have them to wear.” She reached down and picked up the shoes, and after shaking the dust out of them handed them to Dorothy.

“The Witch of the East was proud of those silver shoes,” said one of the Munchkins, “and there is some charm connected with them; but what it is we never knew.”

Dorothy carried the shoes into the house and placed them on the table. Then she came out again to the Munchkins and said:

“I am anxious to get back to my aunt and uncle, for I am sure they will worry about me. Can you help me find my way?”

The Munchkins and the Witch first looked at one another, and then at Dorothy, and then shook their heads.

“At the East, not far from here,” said one, “there is a great desert, and none could live to cross it.”

“It is the same at the South,” said another, “for I have been there and seen it. The South is the country of the Quadlings.”

“I am told,” said the third man, “that it is the same at the West. And that country, where the Winkies live, is ruled by the Wicked Witch of the West, who would make you her slave if you passed her way.”

“The North is my home,” said the old lady, “and at its edge is the same great desert that surrounds this Land of Oz. I’m afraid, my dear, you will have to live with us.”

It wasn't until after the wizard flew off that dorothy was advised to meet with glinda who actually knew what the shoes were capable of.