Clary is a girl with her priorities in order. They might be in the wrong order, but at least they're in order. Here are her priorities.
Two: Jace's clothes and/or getting him out of them
Three: Everything else
When fighting the demons on the approach to Valentine's ship, Jace lends Clary his jacket, because when fighting bloodthirsty demons from another dimension, the last thing you'd want to be is cold.
Clary proves to be more incompetent than usual in this battle, actually getting picked up and carried away by a flying pterodactyl-like demon and dropped into Valentine's stronghold. There, she finds Maia, who tells Clary that Simon, her BFFL, is dead. D-E-A-D. Dead.
Clary's first reaction: That demon scratched Jace's jacket. Here are her thoughts:
It was ruined, the back scored through with a dozen razored claw marks. Jace will be upset that I wrecked his jacket, she thought. I should buy him a new one. (3.18.37)
We're not sure if Clary is in shock at the news or is actually about to pull up the Forever21 app on her phone and order Jace some new leather.