First off, if you don’t want to be a shitty parent, it’s not your choice at all. Now, for a 17-year-old, I can’t really say that they truly understand what it means to be poly, but it sounds like you don’t either. The only thing not being supportive is going to accomplish is pushing your daughter away.

Best resource I’ve found for what it “means” to be poly, https://www.goodreads.com/book/show/52569124-polysecure

I say “means” because love is a spectrum and there’s no true definition.

Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society, then the tolerant will be destroyed, and tolerance with them. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.

-Karl Popper