How strong do the winds have to be to impale human flesh?
I suspect she was chasing it as it was blowing away from her, dragging in the sand, and just as she caught up to it, it tipped and she ran into the bottom spiked point angled upward at her. The top of the umbrella would have been anchored in the sand.
She was probably wearing a t-shirt or a tank top and the cloth didn't offer any resistance to the spike. Her forward momentum tipped it up further until her weight impaled her on it.