Summer units help

try your luck once again for better IVs. Muahahaahaa

For Cordelia focus on her speed and defense with speed/defense refined Slaying axe giving either 41/31 or 38/34 speed/defense letting her work on either phase. With cavalry buffs she basically can't be doubled and can hit back with 2 turn Luna/Bonfire. If a change of weapon isn't possible due to lack of fodder, run Quickened Pulse or Moonbow.

I can't help with your Cordelia problem, but I had a similar problem with my innes (+hp-atk) and someone helped me come up with a more defensive build for him. The build used slaying axe, brazen atk def for boosted offenses, any rally skill, bonfire, def feint to debuff and thus do more damage, the C skill can be whatever, and the seal was atk/def. The idea here is to bait the opponent into hitting innes, then counterattack with bonfire to deal massive damage thanks to slaying axe and innes high speed. Now that's a defense oriented build but if you really want to use the restroom, you could switch brazen for distant counter, make the seal distant defense, make the C skill atk ploy, and switch the special to iceberg to use all that res to your advantage (idk if iceberg has a 3 cool down count, if not use the res based 3 cool down special, maybe it's glacies idk). You still need slaying axe to proc the special. The idea of waiting out the opponent and getting a special remains the same. I think either build would work pretty well, I know the first one does
Hope this helps!