I am Tim and hope can help you. I am not a doctor so am only giving you my opinion. Quickly about me,, I had a major stroke in 2010 and a year later epilesy. So that being said, I think your sister had a seizure and may had epilesy. Especieally that you said she lost control of her bladder. That is very common with epilepsy.
Please don't think of the worst yet. Don't think tumor. But she must see a nuerologist. They only deal with our brains. I was in the hospital 4 times last year and not doctor new what was going until I saw a neuerologist took many tests and I had epilesy. With medication, I have not had a seizure in 7 months. The drugs are really hard at first, but you body gets used to it. And I would rather take the drugs now that have another seizure.
Like I said. I have know idea what is going on to your sister, but just from my experiences it seems it could be possible. I only wish you both goodness and happiness,