How much Determination does Frisk have at the start of this fight, exactly? Just base level DT? Well, regardless, it's completely impossible for Buddy to win, as far as I can see. She isn't stopping Frisk from using their SAVE file to come back after every death, can't BFR Frisk, and I doubt they could incapacitate Frisk to any extent, especially not for so long that it would constitute a victory. Buddy has higher stats normally, from what I can see, but Frisk wins at the end of the day because of Determination sauce.