It’s not easy for me not to give a fuck about her, Even.
I think Grillby would be more relieved than angry Aster. He's mad because he thinks you lied to him remember?(In addition to the Crispy situation). Besides Grillby is a good guy, he's not going to hold it against you or Sans just because he was created and not born. Grillby loves Sans! And even if he doesn't take it well at least you'll know you did the right thing by telling him the truth.