Yuka didn't know what a frost giant was, exactly, but it painted a picture of some pretty incredible strength. Where would that put her own strength? 20, 25? It's hard to guess without a proper frame of reference.

"Maybe that's why my enhance ability affected you so much. It seems to make Kyouko about twice as strong, so maybe it increased your Strength to a 58?" More likely, from a +9 to a +18 modifier.