I'm absolutely a proponent of parents and school personnel being a team.
But this is one area where checks and balances should probably come into play.
If this topic is taught both at home and in school, we're guaranteed that the kids have heard the message. So if there's a problem in the home-- a parent, a step parent, an adult's significant other for example-- they know they can tell their teachers. Likewise, if there's an issue from the time they get on the bus in the morning until the time they get off it in the afternoon, they know they can tell mom or dad.
I don't think it has to be overdone, but they should know, as Zelda said, that "no one should ever touch your parts that are covered by your swimsuit unless it is your parents to keep you healthy and clean, or a doctor to keep you healthy."
And the earlier and more often they hear it, the more likely we are to save some kid.
Also, Grammy, if this parent knows her child has gotten the message, but still wants you to cover the material, there may be something she's not saying. There may be another child in the class who she knows needs to hear the message, but she may be afraid to call CPS.... and she's not a mandated reporter.
I think I would begin with a chat with mom.