Toph would need to know Deku can one shot her to put on earth armor, she doesn't lead with it on.
Deku's opening move is that he jumps in the air and shoots blasts at Toph, who can't sense things in the air except metal I believe. She can sense his position, but she wouldn't, however, know that he's also shooting air bullets at her with his gloves, so she'd get hit and lose. By bouncing around I assumed Toph would lead with throwing up earth pillars and columns to hit or move Deku, which he not only has dealt with and dodged before, but can also use for his mobility by bouncing on.
Walls help Toph if she knows she can get one shot and how Deku's attacks work. Neither of them know anything though, so she'll likely start with trying to hit him, while he starts with air blasts. I'm not underestimating her seismic sense, it's been shown that she can't sense things in the air as well as she can on the ground, and Deku fights in the air most of the time, so she'd have to not only read his movements, but correctly judge, for the first and every single time afterwards, that he can one shot her with a flick of his fingers or kick of his legs in her general direction.
Yes he has gauntlets, it's Current Deku, but at 20%, all of his attacks produce wind blasts anyway, all of which one shot Toph. She can defend with earth walls, but she needs to not get one shot the first time and every other time afterwards to win.