Female duck behavior towards ducklings

[Terraalexandria]

I have slowly introduced ducklings I incubated to our older girls and one seems to (what we first thought might have been trying to sit on them) but now we are convinced it’s aggressive behavior. Almost seems like she’s running over our ducklings.

what could it be?

 

[Crazy Maizie]

It might be too early for a full integration. How did you go about integrating? How old are the ducklings? How old are the "older girls"?