Helen enjoys being in the garden because she can be guided by touch and smell, since she cannot see or here.
As a child, Helen seems to have enjoyed nature even before she lost her sight and hearing. After she lost those senses, she appreciated the garden because it allowed her to experience pleasure and sensory overload.
What joy it was to lose myself in that garden of flowers, to wander happily from spot to spot … (ch 1)
Helen may not have been able to see the flowers, but she could smell their perfume and touch their delicate shapes. She could feel the sunlight on her face, and climb the tree.
I recognized the odour of the mimosa blossoms. I felt my way to the end of the garden, knowing that the mimosa tree was near the fence, at the turn of the path. (ch 5)
To Helen, the garden was beautiful not for its colors but for its smells, textures, and tastes. In the garden she could close her eyes and enjoy nature, pretending to be like everyone else. It did not matter that she could not see or hear it.