From Maggie's perspective, Beth is most likely dead. At best, she's lost out there with no possible way to find her... but she's probably dead. There's just no way to know for sure.
Glenn, in comparison, was on the bus--- she had a lead on his last location. When his body wasn't found on the bus, it gave her that ray of hope that she probably completely lost after the prison fell. She had reason to believe that he was alive and to continue her search for him.
I believe when Maggie's "tunnel vision" took over, she blocked out all of the atrocities that happened at the prison. Her father's death, as well as her sister and all the others probably being dead, would be such a heavy, difficult thing to handle. I can believe that she was blocking that out best she can until she could find Glenn.
What it comes down to is that Maggie had reason to believe Glenn survived and that was what gave her a reason to keep going. Now that she's accomplished that goal, I'd have no doubt that the weight of the horrors she's been blocking out will start to come crashing down on her.
People grieve in different ways.
I also wouldn't be surprised if there were a cut scene or two with Maggie talking about Beth and Hershel, or Tyreese about Sasha, etc. but could have been deleted for time. I feel like actors and producers are always talking about all kinds of scenes that get cut, and most of the time it's probably dialogue.