Who did Mary Magdalene think the risen Jesus was when she first saw him?

Answer: The gardener

Thinking He was the gardener, Mary asked where the body had been put. She recognized Jesus when He said her name.

““Woman, why are you weeping?” Jesus asked. “Whom are you seeking?” Thinking He was the gardener, she said, “Sir, if you have carried Him off, tell me where you have put Him, and I will get Him.””— John 20:15 (BSB)