change in behavior

Question
Hi! I have a question about my aunt and uncles dog, Ellie. She is a mixed breed about medium size short hair and around 6 years old. They've had her for many years. We've brought our 7 year old female Brittany spaniel, Dixie out there to play with her for the past few years and they have always gotten along, just a few playful fights. Just a few weeks ago Ellie attacked our dog Dixie but we stopped Ellie. It happened again not long after that and she was biting onto my dogs neck and it was kinda bad but we stopped her. Now they told me that Ellie just killed a wood chuck. We are now scared to bring Dixie out there because Ellie has started this behavior. Like I said, they've had her for many years and she's never acted like this. They're now thinking about maybe giving her away. Is there a cause for this behavior? I don't think it's normal, but if it's how she's going to be for the rest of her life then they may give her away. I'm thinking there could be a reason she has started this scary behavior but I'm not sure. Any advice would be great!

Answer
Hi Kylie....
Any drastic change In behaviour, especially with aggression is cause for concern but not cause 'to give a good, happy long term pet away! All behaviours can be dealt with effectively and where help is needed it should be sourced.
Has there been any changes in Ellies life recently? Is she in good health? Is she generally a well behaved, well trained dog that is loved and doted on? Usually when a dog RE acts like this its thru fear or pain. Has your dog Dixie behaved differently toward Ellie, come into heat or been more intense in play at all?
Giving Ellie away will not solve the concern and if there is an issue it will only go with her to someone else. My advice would be for your Aunty and Uncle to take her to the vet for a thorough medical to rule out a physical reason that may be making her react toward Dixie during their play.
If there is no medical reason then behavioral it is. What needs to be ascertained is why? How? When?
A behavioural trainer or behavioural vet can assess Ellie in her own environment, with Dixie, with other dogs, with aunt and uncle etc. It could be a dominance  issue, jealousy, fear and or anxiety that she is uncertain where she fits in her pack etc so she's intermittently lashing out. Sounds like the events have escalated and thats not a nice thing. But thru a process of elimination you will get to the reason and can then work on  discouraging her unacceptable behavior and redirecting her with positive reinforcement.
Having said this, your family is responsible for keeping her, your dog and other people safe and any escalation in aggression must be observed. With killing a wood chuck which Im guessing is a small wild animal like a ground hog or squirrel? That is probably not anything to be concerned about as you dont know her breed types so highly likely its just a prey drive that many dogs have naturally or she has a hunting breed within. If first one caught in 6 years its not cause for alarm,  just so happened it occurred when red flags had gone up.
With commitment, love,  patience and a good trainers input Im confident Ellie can be dissuaded from this behaviour. But pls rule out medical first as like I said pain, fear, anxiety etc can cause fear aggression outbursts.
good luck, if u can, pls send quick update when you know what's happening? Best wishes Leigh-Anne