What can I do with two Olwens?

You know you don't HAVE to use Dire Thunder, right? Olwen and Ophelia can't even be compared because they can be played differently.

Olwen could easily be given Blarblade (doesn't have to be the +version) and made into a monster, even with an attack bane.

You could give the +Spd Olwen a bladetome and slap her on a horse team.

Definitely don't send home or use for 3* available skills. Just sit on them--it's not like they take up much space. You might come across a good nature in the future and then you have fun merged olwen.

I'd say put a blade tome on Olwen +spd. She has 23 base atk, 36 with Blarblade+. If she receives both hone and fortify cavalry she effectively has 66 atk without an A-skill. Darting blow would give her 49 spd (without a seal), or the standard fury+desperation, or you could even go death blow and try to OHKO people who don't have 72 magical bulk (i.e. a lot of lance infantry) and still follow-up against anyone who doesn't have 38 spd. How's that for you? Olwen OHKO on -atk, no special needed.

Or if you don't want to sacrifice 20k feathers, just use Blarblade (not Blarblade+) and you're running with 4 less atk, which...probably doesn't matter when you're hitting for upwards of 60 atk.

It's also an idea to use +res -spd for ploys by taking fury in the A-slot. You could even put, like, chill def or something in the B-slot, just go full-out support. She'll also provide some coverage because she can still take out certain reds (ex: DC Ayra who one-shots your swordbreaker mages with wrath RA? Yeah let her try to wrath RA against brave thunder. You only get one Ophelia in AA so if Ayra shows up multiple times you'll need multiple counters), Lukas, and possibly some Cherche and Bartre if she manages to quad, which is definitely not impossible with spd ploy. A build like this probably goes on a mixed team, because the play style definitely doesn't sound like a typical cavalry team (not that it can't be done, especially if Gunnthra is on the team)

The other one you can fodder for reposition or merge into +spd -atk.

Actually, even without +res you can take fury and ploy people. It won't be as consistent, but you might be surprised how many people you hit.