And, again, this isn't just something I made up. I was informed of this last year by an editor on my own sex scenes. She said "In YA, always mention a condom."
I don't doubt that your editor said this, but I'd have a hard time taking her rule seriously. There are so many YA books out there that don't mention condoms. In fact when I do see them, I feel like the writer was forced to put it in or felt like they had a moral obligation to do so. I'd be interested to see a poll of editors who agreed with him/her.