It could be anything that caused the seizure, it may even be genetic. If she was having seizures while you were out, eventually you would see signs, such as urinary incontinence, confused states, staring into space, sleeping for long, long periods of time (postictal)
Was it a hot day out? If they are overheated they can have a seizure. Over excited?
I took a year old yorkie to the vet (years ago) she had a seizure on a hot day, they kept her overnight, medicated her for a couple of days.
It never happened again, except for some occasional mild seizure activity as she aged, she lived to be 16.
Anyway, she never needed meds.
But another dog I had, started having seizures at the age of 9 months (after being neutered) He went on a low dose of phenobarb and was fine, he lived a long life too.
