Yes, Lash told Harry as much in White Night. No, she didn't call him star born, that is a term someone else gave him... But she said..
page 363
"It is relevant," Lash said, "Because of the circumstances of your birth--because of whyyou were born, Hary. Your mother found the strength to escape Lord Raith for a reason."
She goes on to say a few lines later;
"There was a complex confluence of events, of energies, of circumstances that would have given a child born under them the potential to wield power over Outsiders."
She nearly confesses to Harry in Blood Rites what she did, I don't have time to look up the exact quote now, but in his vision of her in his soul gaze with Thomas, she speaks of her arrogance to do what she did in creating him.. In Dead Beat his dream about Malcolm he also speaks of the unfair burden he and Margaret placed on him... To my way of thinking that pretty much spells it out that they deliberately conceived Harry to be a star born.
Does that imply that Malcolm was complicit in engineering a starborn? I've never considered that before. That puts a different spin on his character for me. I've never really thought about Malcolm, to be honest, which is unfortunate now that I am. I always kind of chalked him up as a vanilla mortal who got swept up in a romance and found that the world was way more complicated than he thought. But if he was complicit, and there was something specific about Malcolm that Margaret was looking for...
If there's anything to the Five Points of Starborn Genesis idea, maybe it was Malcolm's spirit that contributed? Harry seems to get a lot of his altruism from his dad.
Lash's statement implies that Margaret got the strength to escape Raith in order to make a starborn; did she realize that Raith had Outsider sponsorship? Did one of her contact among the Courts show her the Outer Gates, and realized that the next generation needed a starborn to combat them? Maybe she understood that she'd never be able to make a starborn with Raith, and started looking for someone compatible?
Or—and this is a whole lot of conjecture—did she somehow find out about Nemesis, realized the threat it represented, and do everything she could to stop it? Maybe... after being infected herself?