I have used it on her. Heidi had taken more than anyone's fair share of lies and subterfuge in this family and knowing his mother had used her ability on Heidi, malicious or not, believable reasons or not, was Nathan's limit. Heidi, the boys – they were who he was responsible for protecting the most. He could still try to protect Peter, likely always would, but the combination of his little brother growing up and everything here made that role just one of big brother, not surrogate parent in the face of other parents failing to do their job. And Peter would know he was being manipulated if she did it to him. Heidi would likely know the same, once she had been told, but the boys were too young to know and he still didn't want them to know the measure of what was wrong with the Petrelli family.
He stood, taking several steps away as he attempted to reign in the anger, a combination of stamping down on it within himself and muffling it along the link. He doubted it was entirely effective, as he certain still felt angry and suspicious and way, but he had to make the attempt. Now that he knew this ability, he needed to know the rest, to know what he was dealing with. Later, when he was out of the room, then he would let the feelings loose, would tell Heidi the truth she deserved to know, but right now he needed to keep it together.
Of course, that meant believing her about her abilities, but he knew at least some of this could be verified. Right now, he couldn't give in to the temptation to scrutinize a lifetime – or not a lifetime so much as those parts concerning people he considered to be his responsibility, especially those who hadn't known a damned thing going on.
"And this ability, it's exact, with no room for error?" he questioned, turning back around to face her from the spot he'd stopped.