Is that true that elizabeth masen knew about carlisle cullens secret how did she know wasnt that supposed to be a secret that he's a vampire?

Elisabeth didn't tellCarlisle if she knew or not, but she said "Save my son [Edward], do for him what others cannot", presumably referring to Carlisle being a vampire.
so even if she did know she even knew to keep it to herself (keep it secret) right if she knew keep it secret? did she tell her family that's all?