Look carefully at teshuvot that discuss in-person communication, such as Igros Moshe: is he mentioning an alternative of answering teshuvos in writing? As most of warning is regarding voice, talking, looking, it is obvious that writing is preferred. If there are some restrictions on writing, the poskim should be mentioning those. But this is for necessary discussion. The biggest question on CR would be for silly discussions…
There is also a halakhic consideration of derech eretz that overrides extreme precautions. If you are in a society where people talk, then you should say shabbat shalom and mazal tov; if you live in a shtetl where this is not done, then don’t (most poskim, check with your own). So, ignoring a reasonable post by a lady may qualify as an offense against derech eretz.