I'm not a huge Meghan fan but don't think she's said or done anything wrong here. FWIW, I have two much older half-brothers with a similar age gap between us and have always thought and talked of myself as an only child. Unlike Meghan's relatives, said half-brothers are highly educated, perfectly respectable people, so there's no reason at all to 'hide' them, but I've only met them about a dozen or so times, we don't have a relationship and I haven't seen them in at least ten years.
I also don't see how Meghan incorrectly claiming she's only only child or didn't have a relationship with her half-siblings could possibly be defamatory of Samantha or anything a court could be interested in. Lying (I don't even think Meghan was lying here, but whatever) is not illegal as such and none of it is any of Samantha's bloody business. She needs to go away and STFU.