I am an adult in my late twenties who has been out as non-binary since my mid-teens.
While yes, I am still non-binary, and I prefer neutral pronouns, over time this has become far less important to me as I've become more comfortable in myself. My family still use she/her and a mix of my old and new nicknames, which doesn't bother me anymore and hasn't in a long time. I know they don't mean it maliciously, and it doesn't indicate any disrespect or lack of support.
My advice would be to do effectively what my own mother did; that is, support with clear reservations. My mum did her own research on binding, surgery, hormones and more and we came to some agreements and compromises in my teens about how I wanted to do things and what she was willing to support. We agreed that she would try with my new name and I would hold off on any permanent changes until my twenties, both of which held up. I wasn't allowed to bind for more than a few hours at a time, and we mutually agreed not to bother with changing name or pronouns at my college. My mother is my closest relationship and her support meant and still means the world to me. I also know that if I realised I was actually cisgender that, even after over ten years, she would be fine with it. I've never felt locked into anything by her support, as she's been clear from the start that as long as I'm happy with myself, she's happy.
I have since had one surgery- a double mastectomy- and no plans for any further medical transition. That one surgery eliminated my body dysphoria to the point where I no longer think about it, it just doesn't occur to me anymore. Some of my trans friends have had more medical intervention, and others less. What I'm trying to say, really, is that for a lot of people these feelings get easier over the years even if your DD's dysphoria does persist. Her feelings are big and volatile right now, but they won't always be that way. You can be there for her without agreeing with or supporting every aspect of her gender identity, I think other PPs have made good suggestions when it comes to avoiding names and pronouns if need be.
Wishing you and your DD the best!