Mary, or Zac, or whoever else are only one small part of the issue.
It's not a "rogue employee", Valve definitely has a penned in policy to "not allow sexualization of minors", for one person this can mean on screen penetrative H scenes, while for Mary it can mean high school uniforms, but the point is it's extremely simple for another Mary to just appear as long as Valve's review policy is structured the way it is, and it would be extremely difficult to convince them to "rewrite the policy that rejects sexualiztion of minors"