Definitely cut out all foods/treats with preservatives, additives or colourings. Eliminate all stress from her life as much as possible, be that when visitors call, when the DC are getting over excited, whatever. Stress is a big trigger. Also remove her from the vicinity of computers or vice versa - I've known dogs to fit as a result of the noise from them. Others have found that the smell of pine, particularly that in some detergents, can be a trigger and I'd recommend that you make sure washed hard floors are completely dry, that you don't use air freshener/Shake n Vac and the like in pooch's vicinity.
And never allow her to go swimming - it was a trigger for my first epi dog but even if it isn't you do NOT want your dog to fit in the water, far too dangerous.
Keep a rough daily diary of food and possible triggers too, see if there is anything you can pinpoint.
I'm not too sure about the vet's decision not to medicate atm - sounds like your girl needs stabilising to me. That said I am NOT a vet, I've owned an epi dog in the past and currently have an epi GSD, a long term foster dog whose "real" owner is the rescue. That rescue has a much-respected reputation for it's care of epi dogs amongst its fellow rescue owners, having at the moment 8 or 9 epi dogs out of a total of about 60 pooches. The rescue owner, Dave, is imho an absolute genius on the condition and I'd really, really recommend that you drop him an email or post on his forum (you'll find the email addy there too) and ask his advice. Forum
You can call them too, speak to Dave on 01353 777399 though unless in emergency they prefer emails as they are a two-person rescue who work their asses off from 7am until at least 2am and so are often unable to speak at length on the phone.
My big GSD is on phenobarbitrate, the standard canine epilepsy drug. He has the very minimum dose, 30mg per 12 hours and hasn't fitted in the tear he's been here. The resciue did wean him off it when he was there and doing well having settled in but the fits returned and it was a bugger to stabilise him again.
Another drug which is used but IME vets are less willing to prescribe, is gabapentin, which wards off the "partials" - the staring into space, being "just not there", pre fit. I'd very much indeed recommend that you return to your vet and push for more help rather than let this get out of control.
Hope this helps, if there's anything else you can think of that I may have experienced and which might assist just shout.