Behavioral change

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
Kylie,
It is possible that Ellie has experienced some change in her life.
Has either your aunt or uncle become ill or more infirm?
Has Ellie gotten a little older and is feeling unwell or arthritic?
She is obviously feeling more territorial.
Her teeth may be hurting her also.  If her canines are removed that would reduce her ability to do injury to other animals and would not affect her eating at all.

A visit to the vet would be helpful to see if anything is bothering her.  Also, sometimes there is a pill that they can put her on to suppress aggression.  
It seems she has become more Alpha, for some reason.  It could be just a natural development or due to an environmental change.  Do a little investigation.  See what type of mix she is also.  She may have some guard dog in her that is developing.
Nancy