I have a 7 yr old pit/lab mix and a couple months ago I adopted a 3 month old German shepherd pup. They have been playing and getting along great and when the pit/lab (Voice) does her dominance grown, the puppy, Cheynne, submits immediately. Today, for no reason Voice attacked Cheyenne and would have killed her if I wasn't here. Now what do I do? I don't trust Voice and I couldn't get Voice off Cheynne, I was only able to pull her back far enough for Cheyenne to get away and hide. Voice tried to get her. I finally was able to get her outside. I need to know what to do... I might be giving her away since I have a child.

How old is your child?

Did the pit injure the puppy?

3rd question: Have you ever had any other dogs living in the home since you have owned the pitbull?

*The answer to these questions will help me respond properly as to what you should do.

Not since I have had her... I got the Pit/Lab when she was 5 weeks for my brother. He had other dogs off and on. I just adopted her from him a year ago.

My daughter is 8 and my son is 12... both have been raise around Voice.

Rening, I thought you had a baby. If your children have grown up around her and there has never been an issue, please don't assume there will be one now. If she has been trained properly, she should not pose any threat to your children. Pits are bred to fight dogs, not attack people. If your brother has had other dogs "off and on" that means she became accustomed to being the primary dog in the household. She has now lived with you for a year and has been the only dog in your household. Older dogs (not just pits) usually have a hard time accepting new dogs into the home. She is showing clear signs that she won't accept the pup. I know you aren't going to like this but it is much easier to rehome a puppy than a 7 year old pitbull. Nobody wants an older pit. If you give Voice to a shelter, she will more than likely be euthanized. If you are as concerned as you appear to be for the puppy's safety, you need to rehome him/her as quickly as possible and accept the fact that you live in a one dog household.

I need some answers too.
How old is Voice? Has the pup been altered? Was there food involved (or even in the same room) during this attack? Were any family members in the room or near by? When you say she showed dominant play what exactly did she do and how exactly did the puppy respond? Does voice have any health problems that you know of?
I would suggest using a crate to test the water between the two before rushing to any decisions on either dog. Get one large enough for either dog. Put the pup in and allow the older dog to examine and interact with the pup while the pup is secure in the crate. If she continues to behave like she wants to kill him you might indeed want to try and find the pup a new home.
Lots of things can cause a dominant dog to strike out like this and sometimes it is only a one time event. To effectivly establish who's boss some dogs will seem to go "to far" in teaching this lesson but as a general rule the dog in charge senses (and usually correctly so) that the pup is NOT following the rules of the house.
Sometimes its just a matter of the older dog being overwhelmed with the pups... well puppy like behavior and the older dog is simply tired of telling it to stop so makes the message a bit louder if you will.
Other times there is food aggression or feeling a need to protect a family member.
I actually had a Rottie who was the boss of my bunch and the only female. When she got older she attacked several new female dogs (I had a revolving door for various shelters as a foster home and had multitudes of strays) and each time I thought she was going to kill them. Each time it was only a one time thing. Then one day after getting her furry but kicked one new comer started a fight with this same dog (new girl was a beagle mix and tiny in comparison) and I thought she had lost her mind and was going to die. The fight lasted only a few seconds but that was enough. The new order had been established and my Rottie passed the torch with grace. She was very old and passed shortly there after. It would seem that she knew her days were numbered and as such had spent the better part of a year testing every female that came to our home so that she could leave a successor to the throne in place before she passed!
In short examine every possible extenuating factor before making any rash decisions.

Oh I see the ages now. She is at an age where her playful limit comes much more quickly then a pup and this could be all it is. Don't be distrustful of her, just careful in how you allow them to interact until you get to the bottom of the issue.