1.15 Four Stones In Hand
Mercedes Ruiz is an addict, living in San Antonio, and the sister of Adriana Ramirez. It's revealed in the episode Tracks that she is actually mother to Micki Ramirez (birth name Nina Ruiz). Years before, she had gone to rehab and left a young Micki with Adriana. After three years of being in rehab, Adriana had raised Micki long enough to decide to keep her as her own child. Mercedes attempted to get Micki back, and when denied, asked for money from Adriana so she would not bother Micki again.
Mercedes had eventually tracked down Adriana in 2021 after a lecture. She tried again to see Micki, and when denied she left angrily, and drunk. This resulted in her getting into a hit-and-run accident, which Adriana took the fall for.