Hi and welcome to the Chiari forum.
As Linda said, WOW...it does seem like Chiari is the issue...not knowing what symptoms ur older DD had b4 her DX and surgery, but I am sure it was similar to ur younger DD's issues.
The problem here lies with non Chiari specialist NS's that only look to the size of herniation to classify Chiari as chiari....ugh....the herniation is NOT Chiari , Chiari is the malformation of the skull which causes the herniation...and the length does not matter, what is important is if it is creating a CSF obstruction.
A CINE MRI will show if this is an issue, and other MRI's should be done to rule out Syringomyelia, and disk issues and tethered cord, Then more testing to look for other related conditions such as ICP, POTS, and sleep apnea, and Ehlers-Danlos...as these conditions can affect how one feels and heals if surgery is done, and can cause all the same symptoms as Chiari.....so, if the Drs do not think it is Chiari have them rule out all the others as well.
Not knowing where u r from, I can not say which Drs list u should use, but when research Drs ask if they treat Children as not all will.
Here is a link to our Drs lists so u can use to research.,...the list is NOT a referral...just a tool to use to find the right Dr for ur DD.
http://www.medhelp.org/health_pages/list?cid=186