+Def/-Atk (LA) Lyn

you don't Id use as armor march fodder and try for another :(

If you don't want to pull for another one, just use an Owl tome with +spd, +def or +res refine(depending on the way you build her) and she'll be fine. +Spd and +def are the best for Close Counter builds, while +res is the way to go if you want to use her as a mage dueler. Don't worry about that -atk, if you position her so she gets the whole buff from the Owl tome she'll get to 44 attack, then 49 if you use Attack/Speed bond, while also having a ton of bulk. Use Iceberg as your special. Glacies is another option if you want to compensate for the attack bane with a stronger special. Sacred seal of your choice, maybe Distant Defense, +speed, +attack, Close Defense if you run Close Counter, or even Quickened Pulse if you use Glacies and want to get rid of the extra cooldown charge. Those are just some examples.

Congrats on pulling her!

Perhaps a build that relies on procs..? You could still deal out some decent damage with that, but I would recommend sniping blue to roll another one if you have the resources.