Ah. You don't mean "ignore" like not notice or be in denial about it. You mean that some of the other Carpenter kids might have inherited magical potential, realized it, and then made the conscious choice not to develop it.
Yeah, sorry I wasn't clearer on that, but especially after the problems with Molly if Charity did come clean about it with the rest of her children. You can bet she told them that her talent faded with lack of use. However as I write that, I am wondering, did she ever put that to the test? She might be assuming something that isn't true at all.
Or it could be something else. Hard to know what, though. Perhaps he dug so deeply into the Winter Mantle to fight off the Red King's Will attack that he wasn't himself at all for a brief time. (After, Eb says, "Hell of a hard thing to do." and he responds, "It wasn't hard. Just cold.") Remember that he was acting on a bargain he made with Mab -- if he couldn't bring himself to do the deed, to cut out Susan's heart, it's possible that the Bargain took over his free will and made him do it. He bargained for the power and the time to save his daughter, and he believed that this was the only way to do it.
I doubt that, his free will remained, and I think he cut her throat not cut out her heart. He did believe it was the only way to save his daughter, but it was still his choice to do it. Also there was the realization possibly later rationalization that Susab was no longer human when he did it. If she was, the spell reversal wouldn't have worked.
page 419 Changes, Susan had killed Martin and is in the process of changing. Harry tells her that the Red King wanted to kill Maggie because he death would kill him and Eb, then tells her that she is the youngest vamp and her death can kill them all. Actually it becomes Susan's choice in a way.
Susan looked back at me, her eyes streaming her last tears. "Harry, help me," she whispered. "Save her. Please."
Everything in me screamed no. That this was not fair. That I should not have to do this.
But. . . I had no choice.
Not his choice because he was being compelled to do it by the Winter Mantle, but because in order to save little Maggie, himself, and Eb, he had no other choice than to cut Susan, now the youngest vampire's throat.