I found a picture of her! An old one, from around 2006. She was/is very hard to photograph. The only reason I got this photo was because one of her kittens (at the time) was pretty bold and decided he wanted to nurse RIGHT THERE RIGHT NOW.
...and here's a clear closer view of her face:
...and here are some photos of Shadow where the resemblance to his mom is pretty evident:
Coal seems to have passed down a lot of her overall face shape to Shadow, and Brodie for that matter. They've all got the big triangular ears and the squarish muzzle with the little "pinch" under the cheeks (though Shadow is Mr. Muscles these days, so this is becoming less evident on him). The long tail and body shape both Shadow and Brodie exhibit also seem to have come down from Mom.
Coal's eyes are positioned differently than her sons', though; hers are more straight-set whereas Shadow's go up at the edges like angled almonds (though Brodie's do this even more). I actually only just noticed this looking back at these photos.
When I manage to glance Coal IRL, usually most of what I see of her is her shape. The picture above of her face was a VERY rare and lucky shot.
So yeah, just a random bit of kitty-genealogy there. Which I always find interesting.
(I'm thinking Cora must have gotten a lot of recessive genes as far as physical shape goes, and very likely she had a different daddy than either of her brothers. The main thing she seems to have inherited from Coal is her insufferable cleverness. :P)