Hard to believe with 〜がたい

Grammar Explanation: Difficult to do with 〜がたい

A student from a lower grade enters the classroom. She stops and stares at Asuka Jr., one of the boys in the class.

涼子(りょうこ):: 「ある特定(とくてい)のところに集中(しゅうちゅう)してない？　しかも」; "Isn't she focused on one particular area? And on top of that..."
恭子(きょうこ):: 「ものすごく信(しん)じがたいところに……」; "It's in a frightfully hard to believe area..."