Demelza cried out in pain as Padma summoned her, though she was glad to be getting out of reach of that stupid tree. But it HURT.
But when Padma fell over, despite her best efforts, Demelza was jolted uncomfortably, and she swore. And then she swore again, because she was a bad mood. And again, because she would have to go to the hospital wing, and she wouldn't be able to play Quidditch for a week or two to make sure she didn't reinjure herself too soon. She would bloody well swear if she bloody well liked if flying was on the line!
Wanting to make sure that her saviour didn't get mad at her, she gritted her teeth, and managed a "Thanks for saving me from that tree," which she sincerely meant. Being caught by the tree was enough to never want to encounter it again.