Hello @holly56 I am so very sad to read your post. I am sorry for your loss and wish there were some words that would provide comfort.
My wife had a different type of brain cancer, but I will never forget her neuro-oncology doctors saying on various occasions 'there is more we don't know about the human brain than we actually do know'. In my wife's case we, too, were told it was a rare cancer in women her age as well as from an unexplained cause.
Connect is a large community and I hope there are others who will be able to converse with you on this specific cancer.