Problem with a female Chin and digging

We recently got two female chinchillas that are both just over a year old from a breeder. They both get on fine, but the elder of the two constantly turfs out all the food from the dish they share. We feed them pellets so there seems to be no incentive for her to be doing this. We have tried moving the dish to a different location, giving less food in the bowl and nothing seems to be working. Do you have any ideas as to what might be causing this? And if there is anything we can do to discourage his behaviour coming from her?

Any advice would be appreciated!