Can Janna ACTUALLY Have a cooldown on her Shield?

CD 10 mana cost 110. She ain't gonna be spamming that for long.

Cooldown: 10 at all ranks with a scaling mana cost

she wont have 40% cdr at lvl 1... but lets say she gets to 45% ( taking the cdr mastery ) 10 secs Xs 45% (4.5seconds) 10 -4.5 seconds = 5.5 second cool down at max cdr.. it last for 5 seconds so its down for .5 seconds at max cdr

but if you kill janna then its down for a lot longer

kinda like playing raka blow her up in the fight she dies or is so low she cant heal anything