Because her teaching method is unreliable with 〜ので

Grammar Explanation: Objective reason with 〜ので

ご注文はうさぎですか？ » Volume 1 » Page 87

Syaro asks why Chino doesn’t have Cocoa help with her homework.

ココア:: 「ココアさんは教(おし)え方(かた)がアレなので頼(たよ)りになりません」; "Cocoa is unreliable because of her method of teaching."