What you are seeing is pretty normal. when you have two females, one has to be the boss and one the follower. Normally the resident dog ends up being the boss of the house as most people introduce small pups into a new household. However Pepita may be a pup but would be old enough to be sexually mature. With Bindi being so much older, Pepita may be starting to see if she is more dominant than Bindi. If she is, she might feel she should be the boss instead of Bindi.
The boss gets to tell the other dog what to do. They get privileges such as the "right" to eat first, get affection first and even go outside first. If they want something the other dog has, the leader just has to walk up and the other dog is expected to give it up. This is what it sounds like may be going on. I also want to add that usually when you add a basically adult dog into a household, the resident dog thinks they are just a visitor at first and thus doesn't have much of a problem but as they stay longer, the dogs realize that they are there to stay and then fights can start as they figure out who is the boss and who isn't.
Now I know you think that Bindi is starting it, but it might be as a form of reprimand for something Pepita is doing. For instance, you walk into the room. Bindi, as the boss, has the "right" as top dog to get your affection first. Say Pepita pushes past Bindi in hopes of getting to you first. Bindi would as boss have the right to reprimand Pepita since she acted in a way inappropriate for an adult lower ranking female in a pack. Any misbehavior by Pepita would be met by a reprimand from Bindi. So this could be Bindi teaching Pepita that she is the boss and isn't going to back down.
However, Pepita as I touched on might also be doing things purposesly to test if Bindi can keep the top dog position. If Bindi continues to reprimand her then she may back off and peace will be restored. If Pepita is a dominant dog as well you might have ongoing issues until one is the clear boss and the other totally submits.
Obedience training can help. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
Additional training can also help. Both dogs should be leashed and if one dog even looks at the other dog, a correction should be done. Any sign of aggression including a prolonged look, hair raised on the shoulders, a growl or even a stiff legged walk, should be corrected. A correction is a quick tug of the leash and a firm low toned "NO". Once you have done this couple of times, you should notice the dogs ignoring each other. When that happens, you will want to reward them for the desired behavior. Again, use tasty treats like the hot dog slices. This teaches the dogs that you WILL not tolerate fighting in YOUR pack.
In extreme case, some females have to be separated permanently. I've found that is the case in a few instances. Usually dogs tend to work these things out. Read more on this here:
There are other causes for sudden aggression in dogs such as hypothyroidism. You can read about this here.
I would start training and learn body language to get an idea of when they might be headed for a fight and I think you can get them to coexist. Here are sites on body language.
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Since there have been recalls on certain foods, please check the following site to be sure the food your animals eat is not affected. If it is affected, contact your vet as soon as possible. Have your dog seen if they have any symptoms.