So telekinesis too? No problem.
For me, it wasn't so much the fact that Merry had telekinesis, but rather why she would use it against Clara.
After some thought, though, it makes more sense to me. Essentially, Merry believed that her failure had made Grandfather angry, and the only way to appease him was via her death. All of a sudden she has two strangers showing up trying to rescue her (and thus condemning her people to death, or so she thinks). One of them (the Doctor) is occupied holding a door open, while it looks like the other one (Clara) is about to grab her and take her away. So she uses her telekinesis to ensure Clara can't interfere with her sacrifice.
Once the Doctor convinces Merry that she doesn't need to sacrifice herself to prevent her people from being killed, and that doing so would simply be a waste (his whole speech was solely for her benefit), she releases Clara from her bondage.
Maybe I was just too thick to pick up on this the first time I watched it. But it is a relatively meaty part of an otherwise fluffy (in my opinion) episode. It's a pretty depressing image, though, a society where a little girl who believes she failed is willing to give her own life in recompense.