I used to drive all over the Country for my sales job (70,000 miles per year). I always said that I was traveling with my "Guardian Angel" aboard as I have many stories similar to yours.
And no, it wasn't a subconscious thing. The most striking was a time when I was traveling Southbound on an Interstate and was "told" LOUDLY to slow down and go over the the right shoulder...so I did. Over the hill came a Northbound car flying up out of the median into the lane where I "would" have been had I continued apace.
By the way, my Guardian Angel was great about warning me when I would meet a law enforcement vehicle..never once failed. "Slow Down" I would hear; and within a mile there it was...LOL! Who knew that they would be concerned with that?
I'm pretty sure "she" is one of my Grandmothers, actually...for a variety of reasons.
Guardian Angel and radar detector in one. :)
It might be the same actual angel that was with your grandmother, or group of them.
As for she herself, if she was a believer, she is not an angel; she is a saint.