It's been a long time since I've dealt with post natal care; but,
maybe there's something in this link for you:
http://www.brilliantbaby.com/html/seizures.html
Yes. I have seen infants have seizures. Sometimes, there is a cause and sometimes it's a one or two time thing, goes away, never to return.
I'm sure they will run exhausting tests, either there or at a Children's Hospital in your area.
I wish your sister well.