You have 100% legal liability for the damages your dog does - regardless of if it is a pit bull or a poodle.

Get in touch with your homeowner's / renter's insurance agent and let them know that this has happened. The liability coverage on your policy will cover the cost(s) to the injured party to pay for their vet bills and the replacement cost of their dog --- and this will keep you out of civil court when the owner of the small dog your dog killed asks for damages.

There is nothing anyone can help you with as far as any court date for the vicious dog attack. You had a dangerous dog roaming loose, so you are going to need to pay the fines for having the dog running at large. The dog has already been euthanized, so there is no need to get an attorney involved - pay your fines. And chalk it up to a terrible life lesson you have just learned about responsible dog ownership. Two dogs are dead now.

Next time you go to save a dog - Think seriously about what you are doing. Do not adopt an animal that is a danger to others. You knew that she was a fighting dog - she wanted to mangle and kill other dogs - and you brought this dog into your home anyway. You can not "love away" gameness, prey drive, or the want to fight out of a dog.