Hi there - I'm Dr. Sara. I'm a licensed vet who works exclusively with dogs and cats. I'm really sorry to hear that your pup has been having such a rough recovery from his procedure.
Cocker ears can have absolutely terrible disease, which is likely why your vet recommended the ear canal ablation - this usually improves their quality of life by leaps and bounds! It's overall usually successful and without complications, however just like in any other type of medical procedure, there can be a small number of dogs who have complications and difficulties after surgery. The first I'd consider would be trauma to the vestibular system, which is the neurologic system that controls balance. Part of the vestibular apparatus is located within the ear, so any type of ear surgery can potentially cause post-op vestibular issues. If infection is involved, antibiotics may be needed, however many times it's just inflammation from the trauma of surgery and anti-inflammatories can help. An experienced surgeon typically is going to have fewer complications, although sometimes these sorts of things can happen even to the most seasoned veterans.
Besides damage to the vestibular apparatus, it's certainly possible that any type of anesthetic event could cause neurologic symptoms. Whether it be a blot clot or thrombus that blocks circulation to an area of the brain or some other idiosyncratic (random and unpredictable) drug event, these are VERY rare, but can occur.
The best place to start, if you haven't already, it with the vet who did the surgery. They know best how to handle the complications. If you're unsatisfied with the treatment she's receiving so far, it's never wrong to consider seeking a second opinion. I would aim for a board certified veterinary surgeon if you're going to get a second opinion.
Unfortunately, it's very likely now just a matter of time and supportive care to get her better (based on what you've described).
Please let me know if I can answer any follow up questions :)