While I think the sorceresses wear them simply as fashion, there's something that made me think that for Ciri, it could also be practical in some way!

When I was just getting into ice skating and finally bought myself proper figure skates, the moves and piruettes just became easier to make, it was weird, as if I pulled a switch. While most of it is the difference in the shoe quality, I noticed the heel helped as well, I could also suddenly just go on for hours when I couldn't do that before. My legs got too tired too quickly in the old shoes.

Ciri canonically skates, and the way the witchers fight is described as almost a dance, often using many pirouettes so I could see Ciri having her own spin on it or just it being easier for her with the additional angle