As Sir Walter's friend and an overeager admirer of Mr Elliot she is indeed a terrible judge of the character of men
Regarding her evaluation of young Frederick Wentworth! Even if
his prospects were uncertain, she could have tried to find some evidence of his character and, considering Anne's devotion to him, maybe looked upon him in a different light. Advising a long engagement or that the young man return when he was more able to support a wife.
With such friends who needs enemies? as the saying goes...