Make sure you keep documentation on this and anything further - print out everything you've sent, all the responses you recieved, make sure all of it has dates, and put it in a folder.
If you hadn't, I would still contact the PTA president and politely let them know that there was an incident, you have contacted the school and they are handling it, and you are concerned that it should be kept private out of consideration for everyone involved. (Having been a PTA president, it is hard to stay on top of stuff like this, especially if you don't know what it is about or who is involved.) Sometimes there is a social media webmaster, and they usually have a posting policy.
Here is ours, for reference:
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