She must consider the fish food as high value and she was resource guarding it. Unacceptable behavior when she does it with you.
Try the following exercises to stop resource guarding.
Remove all treats, toys, bones from the floor. Do not allow the dog any treats, toys, bones or food until he has earned it. I recommend keeping all dogs separated while eating until the behavior is resolved because they may fight.
When you feed the dog, do the following:
Step 1.
Make them sit and watch you prepare their food. Put a little bit of food in the bowl, while they watch you. While they remains in sit, place the bowl on the floor. Tell them when they can eat. Point your finger at the bowl while having them look at the food, then click your fingers and tell them to "eat".
When they finish, repeat. Once they have perfected that task, then move onto to step 2.
Repeat Step 1.
Step 2.
While they are eating, put your hand closer and closer to the bowl and eventually put your hand in the bowl. While you do this, add a few pieces of food each time. Repeat Step 2 until they no longer growl or show teeth.
Re: treats/bones/toys. Give them those things while they are in the crate. Have the other dog(s) walk by them and sit by the crate while they have the treat/bone/toy. When they start to growl, tell them "no" in a calm, stern voice. Do not take the treat/bone/toy away from them because that is reinforcing the fear that someone is going to take it. Continue this exercise until they stop growling while the other dog(s) are around.
Once they have perfected the previous step, move them out of the crate. While on leash, allow them to have treat/bone/toy. Allow the other dog(s) to walk past. Give a tug of the leash if the dog growls. Tell them "no" in a calm, stern voice. Continue the other dog(s) walking past them until they stop growling.
This will require lots of patience. Consistency is key.