Both Springers and Cockers have problems with epilepsy. I did not know this before getting the Springer. I knew that they can have problems with hips and eyes (as many breeds do), but I never saw anything about epilepsy when reading about Springers before we got her. Show-bred Springers also have problems with a Springer Rage Syndrome that seems to stem from one male, but it doesn't show up in the Field-bred ESSs.
The problem here is that you've got the seizures AND the meds on top of whatever training problem there is. Sometimes it's hard to disentangle them.
There shouldn't have been deterioration of the training as the dog ages -- my experience has been the exact opposite, age brings calm and better obedience (at least until they become senior dogs, then they take shameless advantage.)
If you've removed the "pity" factor - i.e. treat her like any other dog - then what's left is probably neurological.
I would consult with your vet and with the trainer about possible changes in strategy to accommodate those. My own inclination would be LONG walks with plenty of work and mental stimulation - for Labs, that would be periodic marks and blinds in the course of a 2-3 mile walk.
I don't know if I'd rule out the Ecollar completely - perhaps consult with the vet, then carefully collar-condition her and keep it on a very low setting - you shouldn't set it where the dog vocalizes or jumps, just look for a blink or hesitation. On a good variable-intensity collar (Tri-Tronics, Dogtra, Sportdog) the lowest setting is BARELY perceptible. I always test a collar's settings against the inside of my forearm before using it on my dog. And good collars have a separate tone button that you can use as a warning before hitting the red button - one of my dogs NEVER gets nicked anymore, she knows when she hears the tone that it's time to shape up.
Given that kids and a lot of work are also in the equation, re-homing may have to be an option. I wouldn't rule that out, so long as you can find a good placement. If there is a local rescue devoted to Springers I would give them a call. Our local Lab rescue is run by a lady with an immense amount of knowledge (former Master Nationals handler) and she almost always has a solution for just about any training problem.
My really hard cases have been terrier mixes and shepherding mixes—both of which need work as stimulus (like field dogs) but terriers and shepherds will also stare at their master for commands—so eye contact works very well with them. No harm trying, I guess. Our Newfie/Lab cross will automatically look away if I tell her NO, but then she can’t look the cat in the eye, and the cat is smaller than her head. Like all labs, she’s kind of dopey.