She's acting stupid AF. I understand she's been beaten down bla bla bla. Lewellyn is absolutely stupid if she believes her step mother is going to allow a threat to her son to exist outside of her control.
First of all she literally only HAS power through her son. Right now she runs everything with her son under her thumb. Presumably when he's properly married she'll still be in a high position of authority in the Government.
Lewellyn is threat to that, and now she's a threat to her new Grandson. Even if she DID vanish into some ignoble exile, she'd still be able to rally supporters around her, or worse, gain reputation of her own that would make her step mother look bad in comparison.
I don't know how much political training this girl has had but she needs to stop being a petty bitch. She needs to start channeling Rashta and she needed to start doing it years ago.