At age six months, the dog will adjust, and you do not need to feel bad about this. Even if the dog were age three, she would adjust. We just went through this with a one year old dog, and the dog was also not like our other dogs, either. This dog was very active and wanted to chase and likely kill our cats. We just could not keep the dog.
You should not feel bad. It sounds like you were trying to protect the dog in the first place. If you know the people, then that is good. Let them know that if they find they cannot keep the dog, you would like them to take her to an animal rescue league, or contact you.
If you find these people cannot take the dog, then contact an animal rescue league who can help find a home and will interview anyone interested in adopting her. These groups are known for being very thorough in looking at anyone interested in adopting an animal. They look at the lifestyle of the people interested, as well as records on how they have cared for previous pets. You can find these groups by going to your pet supply store on the weekend and bringing the dog with you. Seek out the rescue groups showing their pets there, and plead for help. DO NOT call them, because they will say they are full and cannot help. They need to see the dog and then feel sorry for the dog and what is happening.
I will repeat: If you call, text, or email a rescue league, 95% of the time they will tell you they cannot help you. You need to go in person with the animal.
In the meantime, keep the pup in a cage to give the other dogs a break. They are likely jealous and have not adjusted to her presence. If a rescue league offers to allow you to be the puppy's "foster" while they find a home for her, try that if you can. Any help a rescue league can offer is help, and much better than a shelter where you just never know what will happen. It is also better than you rehoming on your own, because they have experience. BUT, if you want to to it on your own, ask for vet references, and go to their home to see where the dog will live. But, people are very good at misleading others, so using a rescue league is better.
The dog will be fine, and likely better than what you are experiencing right now in worrying and in trying to adjust your life to having a dog who is not working out for you.