I think it all started that Thursday night she was working.
Just the way the supervisor described her (I don't believe the supervisor was being over dramatic), something of a traumatic nature happened to Maura and no that doesn't necessarily mean a phone call triggered it.
Whatever it was, she went on a rapid down-hill spiral from that point on.
Her father (IMO) really knows a whole lot more as to the condition of his daughter that weekend he whisked into town to be with her.
I think he did his best to try and calm her down and maybe when he left, felt like she was in better shape. But obviously that wasn't the case. That is what I think his biggest regret is. Leaving her after being convinced she would work through whatever problem she was facing.
Yep- reminds me of that quote from the disappeared programme where he says "And she went into the dorm and thats the last I ever saw of her, which will haunt me forever".