You are right with this sudden change in behavior a good first choice is a vet check up.
Dogs with health issues can change their behavior. A tick carried disease or a low thyroid level can make a dog more aggressive than normal for example. A feeling that she can't maintain her pack role due to illness may make her try to warn off others in the pack so they can't detect that.
If she is not spayed a false (or real) pregnancy can make a dog very protective of her space and toys can become substitute pups in her mind.
Something you can try that will not hurt her and might help her feel a little better if this is a hormonal issue is a vitamin C tablet. 500mg, or 250 mg if she is a small dog, may make her feel less stressed.
You could try some DAP dog appeasing pheromone to see if that helps but before trying that I'd suggest you see your vet with her.
You can read about DAP here
I would keep feeding her apart and that is a good way to monitor how much the dogs are eating too.
If you can dim the lights in the room she is in and keep the other dogs out of there that might help tone down the stress she is feeling.
Hope this helps you!