I taught guitar in schools for many years. Here's a few thoughts you may want to bear in mind
Dunno about recent changes that might have taken place, but county music services used not to like working with kids under 7.
That said, if the student is keen and the teacher/parent is prepared to put in the work (and be patient - a quality you will need in spades), I don't see why not.
Just a few pointers if I may:
1. Start small - as in 1/4 size guitars. There's no point in giving her a guitar with a neck she can't get her fingers round, as it will likely kill her enthusiasm stone dead.
2. I would suggest nylon strung at this stage. (tbh I'm not sure you can even buy a 1/4 electric, and even if you can, chances are it'll be poor quality. Most small electrics I've come across have been absolute rubbish.) Then again, times have changed since I last taught, so things may have improved.
3. You'll need plenty of patience (did I say that already?). When you've been playing most of your life, it's very easy to forget that at 5, everything is new. Early progress is likely to be slow and painstaking, and most of the bad playing habits I've had to try and sort out over the years had been acquired early on.
4. If she can maintain interest, you might want to start looking for a tutor after a few months. As I said, a lot of tutors don't work with really young kids, but if you can find a good one who does, that would be worth considering.
As always in such matters, this is all just my opinion based on my years of experience. Feel free to ignore any or all of it.