Schism, I don't think that counts as not going well. She's six, right? She's little. Changes are confusing for small children, and kids at any age might need time to adjust, whatever emotions that entails. Grieving included. My kid had been holding out for me to marry a woman (I told her I was gay when she was growing up, but I didn't say how) so she could have a girly parent. She was a little crushed at the idea of never having another mom.
Perhaps I oversimplified my experience. I initially told my daughter that it was dangerous to call me "mom" in some certain places. She tried to go along but wasn't good at it. After a week or so of that I realized she thought I was doing some kind of make-believe. So I was more explicit and told her I never was a girl, and that the "mom" part was make-believe. I told her that I'm a boy even though I don't look like it.
I did ask her if she wanted to come up with something else to call me, but she resisted a bit. There was a period where she rather stiltedly called me "dad" and said it way way way too many times in any given interaction, like a bad actor. Once she became comfortable she fell right into calling me daddy. She doesn't call me anything else now.
There was a weird little bit of time when she didn't call me anything. She just clung tight and made sure I was always nearby. It was strange, I'll admit.
One of the main things that helped was assuring my kid that I'm still the same person I was before, and I love her the same way, and that what I'm doing isn't a choice and isn't negotiable. And like I've said a million times, she saw how happy I was, how I finally relaxed, passing pressures notwithstanding. Children read the emotions of their loved ones pretty intensely.