You mean the part where she says Sakuya can make water hot and thus melt ice in the same way? I think it just involves her speeding-up time for the area around the ice so that it melts instantly, not literally manipulating its temperature.
Wouldn't that work by speeding up the particles in the water which are going only so fast, then in less than a second speeding it up to make it hot. Still wouldn't that cause some sort of like instantaneous explosion of energy from the instant particle speed change?