It goes beyond mere frustration; Clara feels completely out of her depth. The Doctor she knows and cares for is gone, replaced by this impostor with a Scottish accent.
She knows he’s the Doctor too, the new version, she watched him change, but she’d expected him to still be essentially himself and he’s just… not.
He doesn’t even make sense when he’s talking. It’s obvious something is seriously wrong with him; the disjointed rambling, the loss of memory, the fact he keeps passing out…
If Clara knew how to fix him she would, but she doesn’t know where to start.