Maia finally stopped after feeling Laz's reaction which is what she was going for. While one might not think of a tree spirit as having any sort of emotions or desires, one must also remember they have never met a tree spirit before.
As for why Maia did this, it was simply because she was annoyed that Laz was treating her as either a little girl or some un-touchable entity. Although he was trying to be respectful, all he really did was annoy her. Perhaps if she had been living her life for the last ten thousand years, she wouldn't have felt this way. But the truth was that aside from watching over her people, she was probably only awake for maybe twenty years towards the end of the war before she was forced to sleep to recover her strength.
At that time, no one would have thought that she would have been resting for so many years as that wasn't the intention.
