So I've been analyzing the Preet screenshot in order to find any signs of forging. I focused on the post count of Fred on it. This is it:
Fred had 36 358 posts on it. Fred currently has 36 386 posts.
Preet first told us about the pm yesterday at 17:28 CET. Fred posted exactly 45 posts from that time which can't add to 36 386. That's why the screenshot wasn't made at that time.
When Preet posted the screenshot it was around 7:00 CET. Fred posted exactly 28 posts from that time which adds perfectly to the 36 386 in his post count.
What does it tell us? It tells us that Preet wasn't preparing the pm earlier after telling us about the PM. She must have done the screenshot between 00:00 CET and 7:00 CET. Of course that's plenty of time to forge it during the night.
But we can also learn from her post activity that she didn't make a single post on tuz between 17:28 and 7:14 which could mean she wasn't here and only made the screenshot when she came back in the morning and got 124023423423 mentions.
Not sure how much this confirms her pm but I think it gives us some perspective.