The only things that leap to mind are Poison/Burn, Ghost Curse, and Hail/Sandstorm. Maybe shenanigans with Sticky Barb and Fling. But all of those things would have required premeditation, which do not seem to apply to the scenario.
[Edit] Out of curiosity, did you try leaving the Pokemon in, and just attacking anyway? She may have still used Endure, resulting in the target surviving the hit. [/Edit]