I'd suggest too, that you cc Katie first. The +5 UP are a better lifesaver in the long run and honestly, the +3 UP she gets on CC are not gamebreaking. Additional she gets +3 Block instead of the former +2 Block. And even at CC lvl 1 she has the same stats as before her CC (at max level naturally), so leveling her up makes her only stronger to hold up against the enemy until you can sortie your archer.

But either way what you are going to CC, only do so after reaching max-level on that unit. Otherwise you break your unit and can't get it to top stats as you will see in the aigis wiki that lolix suggested. That is especially true for Katie, since you only get one copy of her and never again another. BTW, I use Katie for almost all maps and she never dissapointed me.