I have been riding a lovely ID x for a friend. She is a great ride but her only vice is that she spooks at things that aren't there

She can have dogs running up to her barking, tractors teaming past her and not a flinch but then she will shy at a small bird in the hedgerow a mile away or something that I just can't see at all! You get the feeling she is spooking just for the sake of it / to play up sometimes
How would you peeps deal with this?
If you have ever read any of my threads, then I have always said my mare is spooky and evasive. She is however still young (well she is eight, but was backed shortly before she was seven)
Anway, I too have those issues (our outdoor school is probably one of the scariest places to rider her...lol)
The only thing I can advise you to do, is a) Groundwork to de-sensitize her to sudden noises, flying objects and the such like) Just an hour ago i was dragging a bucket around the school...lol
And b) when she does spook, pay no notice and remain calm. I.e if she is playing around a bit or being a little testing then do nothing back and carry on as normal. Easier said then done of course, but never the less it does work. Also, don't know if you do but (I try not to) don't sit there and look for things, or tense up in the slightest when anything does happen, look away from anything she may or may not spook at and just completely ignore it. The slightest tense from a rider, or one that is slightly apprehensive will make such a big difference (not a in a good way) so laugh at it, ignore it whatever you do don't play on it.
Oh one more thing, make sure she is busy as well, so maybe if on a hack some transitions, bending the neck either way for suppleing, leg yielding (if appropriate) and such like, so she hasn't got time to be looking our for potential monsters. And obviously in the school you can do tonnes more things to keep her busy - But moving forwards is the most basic and important one.x
Goodluck