What a wonderful Santa!
I'm an adult of a certain age with child-sized hands (smaller than a few 10-year-old girls I compared them to when one of them freaked out and said "OMG your hands are so tiny!") so my experience may be different than that of a child, who theoretically might have more flexibility than me.
That being said - when I first started playing, I had a Koaloha and a Kamaka and wanted to round out my collection with a Kanile'a. I was fortunate enough to be able to borrow a concert-sized Kanile'a for a few weeks - I'm so glad I did this, because for my little hands it was unplayable! Kanile'as are known to have a heftier/chunkier/thicker* neck than other K brands, and this one was no exception. With my small hands, I was unable to span three frets in first position, making things like Bb impossible.
I have no trouble with this on Koalohas, Martins, or Kamakas, but I have tried other Kanile'as and they just seem clumsy in my hands. Never tried a soprano though, so as RichM suggested that may be the way to go - IIRC they have more frets than most sopranos so that should give her plenty of space as her playing progresses.
Part of me wants to say "she'll grow into it" and don't worry about it, but I'm not so sure. Inevitably when this topic comes up, someone posts a video of a bunch of Korean 4-year-olds playing enormous classical guitars - I'm not sure if that implies that little kids' hands can adapt to big fretboards or not, but mine certainly couldn't.
*Sorry I don't know the proper term, someone always calls me out on this so I'll clarify by saying its circumference measured about 1/8" more than the other two IIRC.