What hoof imbalances can cause forging? Long or stretched forward toes, high heels, too low heels...
If your horse generally has flared quarters, that could be that heels &/or bars are 'run forward' or that quarters have been left too long & under stress. Eg. most farriers trim the wall to be flat from heel to toe on the ground surface & most horses have a natural 'arch' to the quarters, to some degree or other.
If 8-9 weeks is the normal trim schedule, this is probably a bit too long. While 4 weekly may be optimal for most horses, they generally don't NEED to be done that frequently, but IME 6 weekly should generally be max between trims, if you don't want problems. I hear you tho, that both farrier & parents don't agree to that. While I absolutely think you should learn well, of theory and practice first, before taking on trimming yourself, it's not 'rocket science' to learn & do some 'brush up' trims in between farrier visits. Could ask for a rasp & loop knife as a xmas pressie...
I can take, and may be able to post, before and after pictures but that will not happen for approximately another five weeks.
Eight weeks is the normal trim schedule in the fall and winter. This time does get stretched around these holidays. In the spring and summer, however, her normal trim schedule is approximately six weeks.
There is a lot of information, some of which is conflicting, about what is considered a good trim. May you link some articles and/or videos of good hoof practices?
The hoof rasp and hoof knife would need to be purchased online. Would you be able to link them?
Forging is common in harness racing horses, mostly at the walk. Incorrect hoof angles are also common in harness racing here in Western Australia, unfortunately, and if the toes are too long, forging gets exacerbated.
My horse is a Tennessee Walking Horse. She has not nor will be (while in my care) a harness racehorse or a show horse.
Op are you located where it's cold with snow? I'm where there's snow for 6 to 7 months of the year.
If you do highly doubt there will be enough hoof to trim every 4 weeks.
While "cold" is relative, we usually get an average of fourteen inches (thirty-six centimeters) yearly.
We were forced to wait approximately thirteen weeks once. The (new) farrier commented, perhaps complemented, on how short her hooves were. He did not need to use hoof nippers - only a rasp, and he was done in under fifteen minutes.