Hi and welcome to the Chiari forum.
We all are affected by this condition differently.....it is a congenital condition and can start causing symptoms very early in life, but most of what you read states we do not get symptoms until later in life....the thing with congenital conditions, those with them do not know the symptoms they have are not typical feelings/sensations that everyone has since they have always had them do not mention most of them.
As for the herniation getting longer is not the issue, but if it is causing a CSF obstruction, so a CINE MRI is what is needed as well as MRI's of the cervical, thoracic and lumbar spine to rule out other related and non related conditions.
There is additional testing for more related conditions to be ruled out.
As for will she die.....not with the right care....anyone that has major surgery can develop infections etc....and yes there have been deaths associated with surgery and even for those that had not had surgery yet.....most times, they may have done better if they choose a different Dr.
Many NS's will do this surgery......but many should not as they do not research and have it as a focus of their practice.
May I ask what symptoms she is having in addition to the vertigo and headaches?
I had surgery at age 49 and that was in '09...and I am doing well....
If you are told she requires surgery due to the length of the herniation and surgery will fix/cure the problems, RUN away from that Dr as fast as you can...
This can be very scary, and the more you learn the worse it can seem....but with the right team on your side , things should all work out.
Thanks for being a advocate for your daughter and don't be too tough on mom...sometimes we feel like it is our fault our child hurts...and it can be hard to face or hear all that we need to hear....give it time to sink in and help by asking them both to join us here.