Welcome to Just Answer. I'm so sorry that no other expert answered your question earlier. Your question just showed up on the list of unanswered questions that I have access to and I wanted to help. I hope you will rate my answer rather than the delay. My name is Jane. I have been involved professionally with dogs in the healthcare and behavioral fields for over 20 years. I’ve worked as a Vet Assistant and Behaviorist and have extensive experience in dog reproduction, as a breeder, for even longer than that.. Canine behavioral issues and training are also my specialties. It will be my pleasure to work with you today.
It is necessary for me to get a little information from you before I can type up your reply. Your patience is appreciated. Since it is the middle of the night here, I'll probably get you an answer tomorrow morning.
How much obedience training has both dogs had?
Did you introduce the dogs away from the house?
Did the lab move into the Terrier's home or vice versa or did you move into a new home to both dogs?
Is either dog spayed?
Who is the aggressor? If you do not know, let me know the circumstances around a few different incidents where fights occurred.
Normally rat terriers are not that large and labs are rather large, yet you say her dog is the one being injured? Is your dog a smaller dog or a larger terrier?
What have you tried to stop the aggression?