A slug is an infertile egg. They don't always look like the one sadistic serpent posted. The egg in question is most definitely infertile, which means it is a slug.
....Do you mean you have the snake in the shower with you when YOU are taking a shower? or just to bathe the snake.
Those could very well be burns then. The water we shower with is well over 100*F and that is plenty to burn your snake.
Has she been with another snake at all in the last year or so? They generally don't lay eggs at all unless they have been with a male.