Muscovy with runner ducklings

Hi, I have a Muscovy with 5 runner ducklings hatched 2 days ago. Everything seems fine, ducklings are eating well and look full of beans. Only thing that's worrying me a little is that she never seems to  brood them properly. She stands with them under her, I've never seen her brood them like a hen does. She was rehomed here after being found in a road gutter and she has angel wing, but cant see that would stop her from brooding the duckling.Thanks for any help.