No, Mariah is not my pick for fifth Bladebreaker, keep guessing.

Mariah is a member of the White Tigers and Lee's sister, she originally challenged Ray in season 1 but fell in love with Ray losing the battle for her team, she didn't do much after and is far from even being the best female blader losing out to Julia, Mariam and Ming-Ming.
The sad thing is, she's the most qualified to be the fifth Bladebreaker as her love for Ray is canon, so her only role is being ship bait, one of the worst titles I can bestow on a female character.
She's just not made to be anything more and between her and Emily made for a painful run in season 1 for female characters in general.