No one who has any connection to Sara has been shown, she just said she went to see her mother - but she's been out for a bit now and where are those friends the girls met in season 4? They met Emily and Hanna so they would've seen them on the news and been pretty shocked to see their friend, right? Why wouldn't they call Emily to see if she knew where Sara was?
Maybe she is someone else and hasn't actually been going home to her mother? Maybe she is brainwashed like Charles tried to do to Mona? Maybe it's even Bethany Young - Dre Davis' voice does sound a lot like the Bethany recordings..., and is anyone still alive/around who would even know what Bethany looked like? I would be interested to see an interaction between her and Ali, especially after she was forced to be dressed up as Ali for two years underground...
Or maybe she IS Sara but her friends want nothing to do with her because she was so awful to them as Claire said, but regardless, I think it's weird that none of the liars have mentioned it. What do you guys think?