I personally think that all the posts made on Heather's social media accounts were made by Heather.
However, I haven't noticed any that were deleted, so did I miss a lot?
I felt that Tammy referred to 'missing' posts to make out that Heather had posted worse stuff than was viewable. She said that Heather posted 'twisted' things on her accounts which doesn't seem to be the case.
With regard to Tammy having an obsession with Heather's social media though, I totally get that. I had a partner for two years who was a vicious, manipulative narcissist. I found out, purely by chance, that he had been with someone else for the entire duration of our 'relationship'. And yes I got a little obsessed. I HAD to know who this other person was! How could he do that? So I looked her up on social media, read all her profiles, felt little stabs of pain when I saw something that related to him, and probably made a lot of painful assumptions about things that were nothing to do with him at all. I contacted her in the end, we had a long conversation, she had had no idea either. I walked away from that whole situation. Anyway my point in all that is that it's very easy to find the 'other' person and I think you'd have to be very strong not to give in to the temptation.
So Tammy read everything that we've all read. Her world must have been falling apart. And she directed her anger at Heather and not her husband. Which I can imagine is EXTREMELY common. Who knows what Sidney said to her?
Whatever has happened is twisted. However I feel one person out of the two is getting off a little lightly in the media.