Help me to understand what my daughter's understanding lacked.
Can you speak adequately for your daughter? Meaning, do you know what she understands well enough to represent her here?
EDIT: No need to involve your daughter.
Faith is a promise of something real whose realization is in the future (ie, the thing promised is
unseen at the time the promise is given). And when the giver of the promise is 100% capable of making good on the promise, and 100% trustworthy to do so—and when the receiver of the promise
knows this—that newly born faith is also the
evidence that the thing
will be realized. I can offer an example or two if that would help illustrate this in a practical way.
Applying this truth to your daughter, and admitting assumptions I cannot account for without more information, if she sought healing and did not receive it and didn't understand why she didn't, her understanding was lacking
in that she didn't realize that without a promise of healing, she was
not exercising—she
could not exercise—
faith to be healed.
Again, admitting I am ignorant of everything other than the scant info you've provided, I don't doubt her trust in God (her "faith" in God, if you will). She just doesn't know him well enough to understand how he works vs how he doesn't. And so her petition was not answered in the way she sought (to the extent that I understand what she sought).