She is a woman that can mimic anything and anyone in such a way, that you wished the involved ones could not hear her - it is so eerily precise and ironic and such. "Überhaupt" sounds really stupid in that sentence, no idea how to properly translate it. The whole sentence is written very weirdly and I can not keep the style in the translation.

Hi, "nachmachen" means to imitate, to copy someones behavior. "sie hörten es nicht" is a conjuctive clause, it means they wouldn't hear it. I would translate your whole sentence that way (shortened): She is a woman who is able to imitate people to the point that well - you wish them they don't hear it, because it's so pretty exact and ironic and stuff. Sorry, my English is a bit too limited for that sentence but I hope it gives you an impression.