New dog in our home has a sudden mood change?

I am not sure what type of dog you have, but when ANY dog does this it is probably a matter of time before she bites or attacks. It doesnt sound good and I would not trust her at this point. It is so sad, but it sounds like her prior owners were severely abusive. Another thing to do is call the vet and let him/her know that she still acts this way. The vet may do other test and see if she has internal injuries. Sometimes dogs act really funny if they have been abused or if they are in pain for something. No matter what the case is, I would use caution for a while, but it sounds like she needs plenty of love and attention. I would not let her depend on her cage because it will be her way out. You need to hold her if able or sit in the floor with her and give her plenty of attention and love. also, take her outside and play and run with her. This poor little girl is mentally and pysically scared. Please give her a hug for me and I hope this helps you. Good luck.

Did this mood change start before or after the start of heart worm treatment?

I am by no means an expert on this particular medication, but I'd say it's possible that it may have some effect on her neurological functioning which is causing this behaviour.

And if this has started only since the treatment starting, I would contact the vet asap and let him/her know about it.

If that's not the cause, I would contact local rescues to see if they can point you in the direction of a trainer that specializes in shelter/abuse cases. They may be able to help you in bringing her back out of her shell.

For a severly neglected or abused dog, it will take much longer than 1 week to come out of her shell.

She is very scared right now and needs to understand she is safe. It may take several weeks to several months. You just have to keep working with her. But never push it.

She needs to come around on her own terms. She first needs to trust YOU. Separate her from the other dog so she doesn't bite him out of fear.

Sit with her a lot. Get her out on a pack walk with the other dog.

If she is fearful in your home, I would suggest leaving her in her crate in the central part of the house where there is the most traffic. She can observe safely. Get to know the routine of the family. Set a schedule (feeding, walking, going out, etc.) so she learns what to expect. Be very gentle with her. DO NOT YELL. Research confident dogs and you learn how to instill some confidence in her.

She wil calm dow, There has been a lot thrown at her all at once. Since she was not a confident dog to begin with, you have your work ahead of you.

Bathing is a good bonding tool. As long as YOU are not stressed out doing it. A warm gentle bath would be great for her. Feed her kibble from your hand several times during the day to show her hands are kind and rewarding. Get her out on a walk (just her).

This will take time, but it will be very rewarding. Use only positive reinforcement. Remember the tome of your voice and facial expressions are ways dogs read us so remember to smile a lot and reward enthusiastically.

Thank you for adopting this poor heart and soul from her previous life. You are her angel. She will come to depend on you. Guide her gently.

It may be one or both of these: 1) just being rescued from that situation was probably first glad and happy to be out of there and now feeling more comfortable which may allow her to become the alpha dog. 2) I'm not sure what they use to treat heart worms now but a few years ago it was small doses of arsenic which may interfere with the dogs demeanor.

It may have been that when you first got her you may have spoiled her to pieces and given her a lot of attention. However, now she is settled in, your not be paying as much attention to her and treat her like your other dog. She may be jealous of your other dog too. I suggest interacting with her and training. You need to be firm and gentle since she is a rescue dog, but still needs discipline. Since she is sick you may need to take her to the vet or a animal behaviorist, make sure she is happy and relaxed, sounds like she had a hard time. :(

Hope this helps! :)

The dog is sick and a sick or injured dog can act like a wild animal

She's settled in. You either work hard with her, or take her back to the shelter with the new information about her so that she can be rehomed with a more fitting family.

She hasn't been trained. Start training her. She's also very sick, so she's not going to be happy go lucky.