There's a whole strategy you could look up for Winehilde, but considering how close you got to beating her without it, I'd say to try it again and use Sidestep from the merchant job. It lets the user dodge physical attacks. And if you boost before using it, it increases how many attacks you can dodge. Put Tressa in the party and one other person with Merchant as a secondary, make them keep Sidestep up as much as possible, and you can probably stay alive long enough to beat her.
Well... I tried
There's a whole strategy you could look up for Winehilde, but considering how close you got to beating her without it, I'd say to try it again and use Sidestep from the merchant job. It lets the user dodge physical attacks. And if you boost before using it, it increases how many attacks you can dodge. Put Tressa in the party and one other person with Merchant as a secondary, make them keep Sidestep up as much as possible, and you can probably stay alive long enough to beat her.
That wasn’t the strat I used. Just wait and see😉