IMO you have to let her know you know what's going on if it is unacceptable to you and will not be tolerated. If you are going to blow this up and she says "to bad I enjoy it too much to stop" and there is no recourse then don't bring it up.
Straightforward? You have zero control over whether or not she secretly exhibits herself on the Internet and claims she's in an open marriage. You vote with your feet whether or not you accept this. If you don't accept it, state your boundary and enforce it. It's weak and common to state a boundary then NOT enforce it.
It's your call if this is worth enforcing a boundary. If you can't, make peace with that.
