small amount of translucent/clear mucus on dogs vagina?

Over past month I've noticed a small amount of translucent/clear mucus or discharge(I don't know if there consider the same thing) on my 11 year old spayed female's dog vagina, 3 times so far. Her vagina itself is not red or inflammed it looks completly normal. She as also been her normal self, she hasn't been constantly licking her vagina or hasn't been rubbing her hind end on anything except to clean her butt after pooping.