I actually don't think this is normal at all. I'd think occasionally not being able to hold it is one thing, but happening all the time is another. If you are right and she is in fact holding it in too long, that is a whole other set of issues - why is she doing that, and what kind of problems could it lead to in the future?
I am wondering why you were referred to a neurologist for what seems a urological issue. The neurologist appears from what you say, to be approaching things from a neurological perspective. However, I'd try to get a referral to a urologist for this issue before moving forward with any of the neurologist's suggestions.
Given that, if procedures and tests are warranted, they may not be any more fun. I have been through a battery of tests for a bladder issue, including having a scope stuck up my urethra, and it frankly sucked. I won't post all the details here but if you want them, message me. But - the doctor was able to diagnose the problem and develop a treatment plan, so it was well worth it.
Enough rambling - good luck to you and your DD!