Agressive dog

We have 2 dogs, both female (fixed) from Romania. The eldest is 5 years old, the youngest 3 years old. The eldest is quite scared of loud noises and big trucks and stuff, so also fireworks. She is also quite dominant, so she has issues with a lot of male or dominant dogs. She has attacked a dog before because they charged her, but she didn’t bite through the skin. She mostly pressed the dog down and kind of held it on the ground.

The youngest is not really scared, a bit of people, but mostly she’s fine. She is very submissive so there never have been any problems between our dogs. Sometimes a bit of a quarrel but never really a fight.

The past few weeks our elder dog has been attacking our younger dog, we have witnessed this a couple of times now and we are sure our youngest is not instigating anything or attacking the elder one. We have no clue why it happens. They are both healthy. She has peed inside a couple of times. We thought it was because of stress caused by fireworks, but she has actually been doing quite well with the fireworks and it has been a couple of days since new years. She also has had enough playtime and sniff time to decompress.

She doesn’t actually wound the youngest but the youngest is very shaken up and scared after it happens. After a few hours the make up and start kissing on the couch again. They also love to snuggle up together. They are best friends most of the time. If anyone has suggestions on what it could be or how to stop this from happening, please let me know. Thanks in advance.