It’s already too late
A Friesan Draft cross will be heavy, but will wont be a “Frankenhorse”. (Friesans are a light draft horse , really a carriage horse and pretty close to what you would produce with a modern type Percheron).
Even the more modern Percherons still have a heavy front end. The overall shape of the Friesian and a modern Percheron may be similar, but they are still different enough, in competing ways, that it is not something I would ever purposefully cross. Don’t forget this mare is a Percheron x Belgian, so you’ve got even heavier, coarser blood heavy in the mix.
If you keep the horse and want to get papers,
IMNSHO, this foal absolutely needs to get whatever papers are remotely possible to document pedigree at the very least, and if there are multiple choices, which hopefully include 1/2 Friesian, then choose the most appealing, such as Friesian, for a better chance at being wanted by breeding along, regardless of conformation.
Personally, I would change farriers as I would assume that if this happened once it could happen again and you can only afford some many horses :).
Yeah, if there is any option for another farrier, I’d do that. If not, there’s no way I’d leave any other horse, mare or not, unattended at that facility :no: