Daniella always had body issues, both in her weight and her physical disability. It didn't help she's from a tiny town in Utah so pretty much everyone knows about her. She hated going to school, knowing that everyone was looking and talking about her. Her issues further extended knowing she wasn't like 'other girls' and couldn't participate in their activities. She wasn't 'normal'.
Later in life, she became disassociated with the idea of being a girl, as it was putting too much expectation on an identity she had no attachment to nor any way of expressing herself in a meaningful way. So, they started just saying they had no gender, and took up 'Danny' as their main name. Online, they learned more about being like this and discovered the term 'nonbinary' and was instantly attached to it. Ever since then, Danny has been a lot more happy, comfortable with leaving behind the 'girl' label that had caused them so much stress and embraced simply being 'them'