You are not a treatment, let alone a cure.
It’s sounding like her family is inching toward getting you involved again...and they can be oh so persuasive. “You were the only thing that ever really made her happy!” “She really is different this time!” “She was off her meds and drunk, so can’t you forgive her?”
Point is...you’re doing your research and getting educated on codependency. Are they?
You might want to do some planning regarding how you talk to them, as well. They may mean well but dumping her back on you benefits only them.
This is one of those situations in life where enlightened self-interest is the right thing. Get on with your life as you have and enjoy your puppy.
Sending you a hug.