Scripture can tell you what the light is.
John 12:46
I am come a light into the world, that whosoever believeth on me should not abide in darkness.
This is assuming your friend is/was saved the moment she had that experience. I could be wrong, but I don't think an unsaved person would see "the light". Again, I might be a little off here about that.
As for the thoughts, if they are fearful - they are from the devil. Rebuke him in the name of Jesus. Just believe in Christ's offer of salvation. You have it, enjoy it and praise GOD for it, every day! Nothing is more valuable, more critically importan than our salvation found solely in Jesus Christ. No one else, nothing else.
The devil hates you and will try to bombard your mind with thrash. If it is good, it comes from GOD, otherwise all else comes from the devil.