I think the first step to understanding this is to abandon any arrogant notions of them being ignorant or stupid.
Some people just don't like heated argument, as is their right to. Don't forget also that the written nature of internet communication almost always conveys argument with an undercurrent of unintended contemp and sometimes anger.
Perhaps she posted those thoughts in the heat of the moment and, once she cooled down, realised that she didn't mean all that. When you submitted your input, she was too proud to tell you that. And you know what it's only natural to be too proud to admit that you're wrong. It could be the case that she thinks you are right and doesn't want to admit it. No one ever likes doing that.
So I suppose my short answer to your dilemma is that: she isn't stupid or ignorant, she just doesn't want to continue the discussion, for whatever reason. The real danger is you thinking badly of her for that. A contemptuous response towards her course of action is justification enough for her discontinuing the discussion.