It's been a long while since I did do the Sylphie quest line, but I think I might remember other skits. I will place it in a hidden tag just in case it's unwanted spoilers.

I think Sylphie probably thought she might be shackling nature if she drew from that source. She does begrudgingly start to listen when she learns the truth about what happened to her mother doing the same she did. She realized it was a genuine concern for her life from you and the guild master. She also learned that she did not shackle nature at all and felt happy with her new bond.