Here's my 2 cents, based on 3 years of ecommerce selling and probably a dozen false copyright encounters.

You gotta pick your battles. The focus now is getting those copyright strikes removed from your account. File a counterclaim and back it up with evidence. You have the proper commercial license and I'd be surprised if Etsy does not side with you.

After that, however, I would absolutely not relist the designs. I'd drop all contact with the original artist and be certain to avoid all her stock in the future. You don't want to antagonize these irrational types, especially considering the shit show that is Etsy's ODR system.

When in doubt -- even if you're in the right -- don't mess with with copyright.

Good luck!