Unexplained Seizure/Death

I'm really hoping to find answers. My fiancé was 25 when she had her first seizure during her sleep. Luckily, I was sleeping next to her and woke up during it to call for an ambulance. She was foaming from the mouth which appeared to be a clear colored liquid, her jaw was locked, but I was able to move her arms around, she wasn't completely stiff. Her eyes were also rolling towards the back of her head when I lifted her eye lids. She was taken in an ambulance to the ER. Doctors at the ER did an EKG and CAT Scan of her head. We were out of the hospital within 3 hours with negative results from the testing. The doctor said that the majority of their seizure patients are people who've never had a seizure before and this is the first time, and that it is often a freak incident that never occurs again. To be safe, we followed up with a neurologist who did an EEG and MRI of her brain. Again, negative results for any known disorders, and we felt there was no need for medication if it was not recommended or deemed necessary. Exactly 40 days later I came home from work in the morning (I work overnights) and she was laying face down into a pillow not breathing. I called 911 and started CPR. Her lips were blue and the blood had already started pooling around her body. She was estimated to have already been deceased for a few hours. There was some form of liquid on the pillow case which was taken by investigators, but I do not know anything more than that. I know for a fact this was not a suicide, homicide, over dose, or anything of that foul nature. I don't know much about epilepsy and I'm hoping to gain some clarity here to see if maybe this was the cause, or also to learn about potential causes. She was too young for this to happen and its earth shattering. She was in good health and only took birth control and a daily pill (non-narcotic) for anxiety. Help me to understand.