I would have kept the fight the same up until the point where Toph grabs Gaara. Toph sends the mother's sand flying so far away that it can no longer protect Gaara...
...and as she prepares to grab him, she's knocked out cold by a flying kick to the face. Unconscious and unable to counterbend, she's helpless as Gaara attempts the Sand Burial for the second time... this time succeeding.
KO!
That way, they could have kept the claim that Toph could counter all of Gaara's sand manipulation, but that ultimately it only matters so much when you're ALSO against someone that much faster and physically stronger.