Since the horse hasn't been ridden in a while. I or another experienced rider would ride her first. Then after a few minutes in the pen, if she seemed child-safe, I might consider placing a child(is full safety gear) on her and see what happens. Keep them confined to a ring, just in case.
But, just keep in mind, that if she hadn't been ridden in awhile, she may be just a tadbit rusty or lazy.
I like her and she sounds like a wonderful horse. Jump on the deal before someone beats ya to it. Beginner horses are irreplaceable and as stated before are worth their weight in gold.
Oh yeah, don't let the size get to ya. Most of my horses are in th 13-15 hh range. I prefer them that way, they make for better rides and those I have had that were 16-17 hh always seemed to have something going wrong with their feet.
-Kim