Big questions- looking for scriptures to read

Hi! I hope this question is okay to ask. Two years ago my daughter was born with what we now know is a rare genetic condition. It’s taught me a lot about my faith and I’ve worked to get closer to God, as this feels like the only way to make it through all of this without falling apart.

I just wonder sometimes, if praying for something big- like complete healing from her symptoms, is something that God would change His mind on? Like if it’s already written in His will, and He intends it to happen, will my praying do anything at all? And then if not, how do you live with the disappointment of unanswered prayers and still remain full of faith?

I’m just wrestling lately. I do study the Bible but I am new to it. So I would love passages to read, or just any guidance from anyone who has any ideas.

Thank you 🙏