1: The space between the edge of her right thigh and the edge of the front of her dress is colored the same as the surface behind her feet (which is either a seat of some kind or, more likely, the inside of her dress); is Cirno's waist missing, with nothing connecting her legs to her body?

2: It also looks like her panties are missing. Given the ambiguity, I'm adding the No Panties? pool instead of the no panties tag, but I'll let someone else decide whether this also needs the error or bad anatomy tags.

FlameTroll said:

1: The space between the edge of her right thigh and the edge of the front of her dress is colored the same as the surface behind her feet (which is either a seat of some kind or, more likely, the inside of her dress); is Cirno's waist missing, with nothing connecting her legs to her body?

That purple bit is the inside of her dress. Looks to me that the purple part between her thigh and the hem is the part that's in front of her waist; her waist is behind that bit of her dress and thus hidden from view.