Female duck not eating/drinking and is being picked on.

[Carrie Rocket]

We just got 6 female ducks 5 days ago and I noticed that one of them is getting picked on by the other 5 and isn't eating or drinking. She's also seems to be separating herself from the flock on her own. She'll follow them, but not closely. She's also very easy to catch whereas, the others are not. I'm afraid she might be sick. Any ideas for me on what I could do?