There is an underlying reason for why animals (and humans) do the things that they do. Attacking your cat “for no reason” is not accurate. There IS a reason why Tink and Smokey got into it, but it is a reason that you may not understand. Cats, dogs, and all animals communicate in a way that each other doesn’t understand. Learning dog communication, body language, and behavior is SO important when owning a dog, especially a breed that is under such scrunity as our is. You have to be on your guard at all times.
Since we don’t live with you, it will be hard for any of us to really be able to determine what is wrong. We cannot see body language, sounds, and other factors that Tink may be showing that you may not be aware of. Obviously, Tink is reacting to some sort of stimulus in the home. Dogs just don’t change their behavior for “no reason”.
Has Tink been to the vet for a complete check-up? Many times when dogs are feeling under the weather or are in pain for whatever reason, we cannot see it, unless there is vomitting or loose stools. The only way they can tell us is by altering their behavior. If Tink has recently had a clean bill of health (that includes CBC panels, etc.) then it may be something else in the environment.
With behavior such as stealing objects, hiding them under the bed, and growling at anyone who walks by, that sounds like a resource guarding issue. Maybe Tink has fallen in love with certain objects and has chosen to keep them under the bed and doesn’t want ANYONE near her stash. Kind of like a cheetah who hides her catch up in a tree. That is HER stash and she will fight any other critter who comes near it.
One thing to do is to shut the door to that room, and keep the objects that Tink wants away from her. Simple as that. If you don’t want a dog getting something, don’t allow her easy access.
Dogs can begin resource guarding at any age. I would suggest that you get in contact with a canine behaviorist to start to work on the issue at hand before it gets out of control and something really serious happens. Resource guarding is common and many dogs battle through it. If you can start working on it now rather than later, things have a better chance at returning to normal.
In the meantime, restrict access to the areas where Tink is becoming possessive and keep all the stuff that she likes out of her grasp. If she is “herding” you child, sometimes that herding can escalate into nipping and biting. True herding dogs nip and bite at the hooves and legs of cattle, sheep, and the such to get them where they need to go. I doubt that your dog is actually herding, unless she is a mix with a dog with a strong herding drive.
Your dog is a terrier, and terriers have a high prey drive for ANYTHING that moves quick, and that includes children and cats. That drive may have just kicked in more than you are used to. You need to watch your 2 year old and monitor the behavior to avoid anything further than just “herding”. Kids makes noises that sometimes bothers dogs, as do other animals. Tink could have just hit a point where some environmental changes need to occur.
This is NO reason to get rid of the dog. Dogs are not disposable. Get in contact with a trainer/behaviorist and check with your vet for any potential health issues that may be causing Tink some discomfort.