IMO there are numerous issues inherent to Chi's design that makes her and Freya difficult to cosplay.
First off, I think their facial structure and eye design is so soft and stylized that most beautiful girls will simply be unable to look the part. I know the current culture errs towards cosplaying who you like (and not who you look like) and that manga is very stylized anyway but Chi really stands out to me. Someone with a small face, short mid-face and low nose bridge would look best. So like, a 14 year old Asian girl I guess, Chii looks so fucking young.
And lastly I completely agree with the complaints about the hair and fabric. The outfits probably would benefit from nicer, more matte fabrics and the hair perhaps needs like a wire frame or something. Chii's hair was gravity defying and fanned around her, split in the back a bit like a mermaid tail. I can't say I've ever seen a wig frame for 'loose' hair like that but maybe it is possible. Wigs that just limp down don't work.