So sorry you are going through this. This must be overwhelming for your family.
Do you think your daughter will be able to live independently? If not, then you should consider creating a trust. You may be able to change the 529 to a 529 ABLE account, which gives you more flexibility as to how the money is used.
Our situation is different (DS was born with an intellectual disability), but when we were starting this process we talked to Jerry Hulick. He does financial planning for families who have children with special needs. He gave us an overview of the process and recommended several lawyers who specialize in special needs trusts. I’d reach out to him and explain your situation, and he can probably give you next steps or refer you to someone else who can help you.
https://greaterwashington.massmutual.com/about-us/our-financial-representatives/jerry-l-hulick