Incorrect unstable temps could cause issues.
Get this:
https://www.amazon.com/dp/B09DPCW47P/ref=twister_B09LTX95H3?_encoding=UTF8&psc=1
Malformed chicks:
http://extension.msstate.edu/content/trouble-shooting-failures-egg-incubation#CR
Is she hatching the eggs or do you have them in an incubator?
Can you post a few clear photos of the ducklings trying to stand on their own?
And few clear pictures of the legs?