A favorite theme of some people in The Psych World, and others with money-making ministries to finance. If it's a fetish, then it's curable! Either by therapy or by prayer. But the important part is that you accept their premise. That way, they can have influence, and concurrently drain your bank account.
All people have "preferences," certain clothing, a certain look in a partner, a style of car, etc. etc.. A "True Fetish" by definition is some object that is necessary to achieve sexual completion. If you HAVE to have The Panties to "get off," then it's a Fetish!
A simple rule for living, "always question the other person's motive." Especially, when they offer insistant advise or guidance. "Is there some "pay off" for that person? Do they have "An Agenda" that is easy to recognize?" Then, the object of their efforts is aimed at YOU. They want you to become their victim, or their dupe! It ain't easy to live independently, to think for ourselves; but it sure beats being someone else's little slave, always responding to what they want you to do.
Tell The BFF to push that garbage on somebody else. Do it nicely, but do it! The funny outcome? In the future, She will likely give you more respect.
Peace and Love, Joanie