In The Story of My Life, why does Helen consider the old-fashioned garden as the paradise of her childhood?

Helen Keller enjoyed playing in the garden as a young child because she could enjoy it with the senses other than hearing and seeing.

From a very young age, Helen Keller loved nature.  She describes how she used to spend her days playing in the garden before her teacher Anne Sullivan came and taught her how to communicate with the world.  She did not need to have all of her senses to enjoy the garden.

Even in the days before my teacher came, I used to feel along the square stiff boxwood hedges, and, guided by the sense of smell, would find the first violets and lilies. (Ch. 1)

The wonder of nature is that you can experience it even without being about to see or hear.  You can still smell the flowers, touch the grass, and taste the air or the fruits.  Helen had a somewhat unhappy life because she had such trouble communicating, so the garden was her sanctuary.  She often went there when she was frustrated.

What joy it was to lose myself in that garden of flowers, to wander happily from spot to spot, until, coming suddenly upon a beautiful vine, I recognized it by its leaves and blossoms, and knew it was the vine which covered the tumble-down summer-house at the farther end of the garden! (Ch. 1)

When Anne Sullivan came, she told Helen the names of the things that she so enjoyed experiencing.  This just broadened Helen’s experience.  Helen still loved nature, and they would go outside for the lessons most of the time.  In fact, Helen’s first word was “water.”  Nature was a good teacher because it was so sensory.  Anne could teach Helen the word for something by having her feel it and then showing her the word by spelling the signs for the letters into her hands.