Amandla Stenberg as Mami Tomoe (PMMM)

Mami Tomoe is the slightly older and more experienced magical girl who acts as a mentor/senpai character to Madoka and Sayaka at the beginning of the anime. Mami is the archetypal rich girl character and acts with a strong belief in justice and cooperation between people leading her belief in Magi working together as a team is critical. Mami's personality is usually taken to be a clever persona created to cover up her grief (from the tragedies in her life) and feelings about the nature of being a magical girl, although this isn't let on completely and would be done mainly as subtext. Amandla is actually younger than my picks for Sayaka and Homura, but she's taller than my picks for Sayaka and Modoka and with makeup and acting she can easily be a year or so older. I've only seen Amandla in her performance as Rue in The Hunger Games (which was amazing and she did a great job of being both emotionally weak and very confident) i've heard great things about her in Sleepy Hallow another good sci-fi fantasy show. but i was really impressed with her and I think she certainly just radiates the power and confidence In real life too. That would make her a good pick for a live action Mami since those are the qualities that Madoka and Sayaka see in her.