I misunderstood what a 'true' quarter crack was. Apparently they can start from the inside then suddenly just pop out, which I did not know! This sounds like exactly what has happened with my girl Raine.
We have a good farrier that does all the horses here but problem is he only comes every 2 months, and I got Raine just after he had trimmed all the other horses so missed out on his handiwork this time around.
Im hoping its a quarter crack not a hoof canker- those things look absolutely nasty! Praying I never have to deal with that in my future years with horses.