To be fair about the next Death Battle they're using pre Shippuden Gaara, an how many times has the character who seemed obviously stronger lost a death battle? The fact Gaara has Shukaku makes it seem like he's already going to win, this alone makes it so they could make Toph win to be the "unexpected victor".
I wouldn't put it past them to be like "Gaara may have had the edge in the air but soon as he went beast mode and his feet touched the ground it was over. Even with Shukaku it's still completely made up of Sand, allowing Toph to bend it, an even if she couldn't, her metal bending would be similar to how they contained the Shukaku in the past with the golden sand making the sand harder for the beast to manipulate since the gold is heavier than the sand itself, an what is gold? METAL. 'WHAT ABOUT SHIPPUDEN GAARA WIZ?!' Well that would mean we would use Legend of Korra Toph who can still bend things and Gaara also wouldn't even have Shukaku so she could just bend Gaara. In the end Gaara's sand just couldn't sand up, the winner is Toph.
NEXT TIME ON DEATH BATTLE!!!
'Walk into the club like 'What up, I'M MARKIPLIER'
MARKIPLIER VS MACKLEMORE"