She is a former member of the Tower and was a trusted companion to "Mama", until her husband was framed by Georgia and was executed as a result. May and her daughter, Ambre fled the Tower afterwards, fearing the same fate.
Since her escape, May is infamously known as a traitor by both factions alike. Several posters of her face have been put up by members of the Tower per "Mama's" orders around New Orleans, warning survivors to avoid her at all costs due to her alleged "manipulative nature".
After his death, May determinantly establishes an agreement with the Tourist, (AKA you), she leads them to Tower caches, where they can take whatever supplies they want, and in turn they provide her with intel stolen from the Tower.
”It’s about time we met face-to-face, Tourist… I appreciate you gathering me the intel…”