The original question had to be edited down. Phoenix's interactions with the thorns are interesting in light of her characterization. The thorns represent obstacles for her to overcome. They are impediments that make her journey a difficult one. They grab a hold of her clothes and challenge her ability to move through the path with ease. In this sense, the thorns represent those challenges on any "worn path" that make the journey almost as significant as the destination. The thorns reflect how committed Phoenix is in moving to her end purpose, as she is not deterred from her purpose on walking "the worn path."
Phoenix's reaction to the thorns is also very distinctive. She does not curse the obstacles. She does not outwardly reject them. Phoenix recognizes the purpose of the obstacles, almost acknowledging their own right to exist: "You doing your appointed work. Never want to let folks pass, no sir." In this, Phoenix has taken an approach to the world that acknowledges the purpose and function of suffering and challenge. This mature element of Phoenix's character is revealed in her approach to the thorns as an obstacle. She understands that there is purpose in the world and even obstacles possess it. Her encounter with the thorns shows this.