It can be so difficult to watch your child enter new territories or make choices that are not familiar (at any age!). The fact that she is open and sharing these things with you likely means that despite your concerns, your daughter sees you as someone she can talk to. So keep doing whatever you’re doing that’s making that happen!
One important note is that you are witnessing various aspects of your daughter, and some are under her “control” so to speak, but her identity (who she is) and sexual orientation (who she is attracted to) are not. Although these pieces might come into awareness later in life or be disclosed as a child hits puberty or adulthood, people are generally born with a sense of who they are (gender) and who they are attracted to (sexual orientation). Other aspects you mention, such as piercings, tattoos, and polyamory are related to choices she is making around aesthetics, her body, and how she wants to be in relationship. These may shift and change as she explores or matures, as opinions or preferences often do.
One final reassurance is that despite all this, your daughter is still the child you know. If it feels like you’ve lost touch with that person, ask her about what she is experiencing and how she feels about it. If you are able, during this conversation, choose “I” statements (“I’m scared when I think about you doing XYZ” or “I’m curious about what you think about XYZ” instead of “why” questions (“Why would you want to do XYZ?”) This approach reduces the likelihood that someone will feel questioned and then defensive about themselves.
This is no easy task, so be gentle with yourself and keep trying. Remaining connected in your relationship with your daughter will be the most important thing you can do for both of you.