Hi and welcome to the Chairi forum
I know it is easy to get overwhelmed and frustrated trying to navigate this condition since it is hard to know what all is going on when there are so few Drs that are well informed and educated on the condtion and comorbid conditions.
It's possible the symptoms relating to her Chiari is causing the delays.....for example, when I was an infant my mom would put me down for a nap and try to alternate which side I slept on, left or right side of my head....everytime she would change my position and came in to check I was turned back the other way....the Drs told her not to worry if my head was flat, I was a girl and my hair would cover it.....my point is, even thought I could not say what my symptoms were, I knew enought that something hurt with my head turned a certain way, so I moved to avoid the pain. I am sure that your little one may be avoiding how she feels doing certain activities which may cause or lead to a delay...most Drs are only looking for a clinical DX or reason instead of connecting the dots as they were.....
Does your little one spend a lot of time on her tummy? Or in a seat of some sort? I am not sure this helps you or not....but once you find a true Chiari specialist , things will begin to fall into place as to her delays, and a course of action for her.