Hi, I can help you with your question today.
Aggression can start for different reasons.
If you think that you began to notice it around age two, it was likely coincidental with her spay.
She was an adolescent at that time, and we can see many behavior changes including dominance and aggression at that age.
If she is getting worse now, I would be concerned that she may have another medical condition aggravating her problem.
For example, if a dog has degenerative joint disease or arthritis, they can become more easily angered, etc.
I recommend having her evaluated by your regular vet.
I would start with a physical exam and senior blood profile.
We may find something from these that will indicate why she is becoming more aggressive.
If these are normal, I highly recommend speaking with a board certified veterinary behaviorist.
They will be your best chance and behavioral modification to control her aggression.
Of course, you have to weigh the risks of entering a course of action like this as opposed to humane euthanasia. There is certainly risk that you assume, knowing that she has aggressive tendencies.
If you do not feel like you are making progress with her in the next several months, the risk might be too great.
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