I'm having the same issue sadly :( The last person I spoke with before reaching this barrier was Andy, I held off on starting the conversation with him until after I had spoken with Sam and prplsqrl. After he marked Away there was no other apparent way to progress.
Ah, curiously, I restarted the game and something very different happened compared to when I was originally playing; originally, prplsqrl's spot on the Millenium Net Chat didn't even exist at all until AFTER I had found the private message on the PGFH forums and clicked the "add friend" button. With this restarted version, their icon and chat (plus pings) were viewable from the get-go. Whereas before I basically had no idea they were a part of the game until I found that private message. Might be a totally unrelated issue? But also hope this helps in some way, haha.
That was the same for me, but I had found the private message my first try at the game and was able to add them as a friend, but Laguna still never messaged me :( I’m wondering if completely scrubbing the game from my computer and redownloading might help, but I’m not sure where the game stores it’s other data. When I delete the game folder and redownload it everything I did (adding prplsqrl, all the reminders etc) persist.