Having more than one makes it more difficult. I would work with her separately.
Sit on the floor with her and hold a treat in your hand. Tell her to leave it
and make sure she does. When she does give it to her and praise her.
Do this until you feel comfortable and then allow one other dog in the
session and work that way, of course giving both dogs treats. Her first
then her sibling. When your comfortable with that add another dog.
How many do you have?
If she starts to take from the other's start again until she listen's.