Is this manga being translated using MTL or AI? The gyaru's name is AyaSA not AyaCHA. Rua calls her Ayacha in katakana in the raws (アヤチャ) but everyone else calls her Ayasa spelt in kanji (彩茶 and occasionally with the reading explicitly given in furigana as あやさ).
I'm guessing the machine doesn't recognise the furigana and transliterates her kanji name as Ayacha because the 2nd character 茶 is most often pronounced "cha" rather than the alternative reading "sa" which is rarer. (This is also probably why Rua calls her by the nickname Ayacha).