Nope sadly not that unfounded,my ex racehorse broke my neck doing something very similar.I was lucky (apart from the neck, and bleed on brain etc) but I could so easily have been killed like this girl. So awful for her and her family. I can sympathise with how horrendous it would have been when it bolted.
But...yes everyone who points out not all ex racers are nutters is right. Just some do tend to run flat out when get panicked (sadly mine is one of them, but i still love him).
And my ex-racer is a plod, gets taken the mick out of cos he walks so slowly and happily walks down the A414 with drivers being complete nutters alone or in company. Never has the race instinct and when galloping with others is the easiest to keep hold of and behind other horses, and easiest to stop.
Must of course be the breed and nothing to do with individual differences
I honestly believe that you can't condemn TBs as more dangerous as opposed to horses that are like that have that in them, ex-racers, shetlands or anything in between! Just like Chihuahuas, Yorkies or JRT are just as likely to be biters in the wrong hands than Rotties or Alsations.
My deepest sympathies to the woman's family, it could have happened to any of us