Remember Alison’s four visits? You can rewatch them here.
Now pay attention to the reasons why she visits the girls-
Hanna: She’s worried and needed to see her.
Emily: She missed her and is worried (and maybe even saved her).
Spencer: She needed something from her and didn’t even want Spencer to wake up.
Aria: She steals the diary page from the doll, didn’t plan to wake her up either.
I think this is what Grundwald was referring to, not being sure whether Alison could trust them. Either Spencer or Aria, or maybe both, did something to Alison which got her in the trouble she’s in now.