From Halopedia, the Halo wiki

Alizée is an associate or friend of Dr. Catherine Halsey, mentioned by Halsey in a family tree-style picture listing her most significant relationships in her journal. Precisely who Alizée is, or whether they are even human, remains unknown. It is possible that Alizée is an AI, as they is listed at the same level as Kalmiya, another AI.[1]