She had originally intended to do this the straightfoward way which involved no one knowing but her and her mother - tell Carlota that they'll raise her and her husband after all, wait for her to tell her friends, petrify her and her husband, keep them in a demiplane for a century. It's not even that Evil.

But her mother is far more invested in relations with her archmage allies than she is in Lilia (correctly so; the archmage allies are far more valuable than Lilia, who her mother could produce again with a little investment even if she gets this one destroyed), and does not want to endanger relations with her archmage allies by appointing Lilia a duchess without their knowledge, and points out anyway that the Cotonnets use Nefreti Clepati as a babysitter and it'd be just like Nefreti Clepati to say something about it in passing one day.

So she goes to meet Carlota for drinks again.