A PC successfully casts Beast Friend on an NPC's horse while the NPC is riding on it (e.g. charging in battle). If the PC now suggests the horse to run away or lie down, does the horse simply do that, or does the NPC rider have a say in that?
The rules use both the terms "control" and "guide the actions". In the first case, I would see the rider having no more control over the horse, while in the latter I would believe the rider might counter with a ride check who has a better grip on the horse.