I'm so very sorry.
Honestly I don't know why the vet said it was okay to feed plain chicken right now. It's not because her liver is having such a hard time. She needs to be on a very low protein diet. Maybe the canned L/D? Either that or an emergency consult with a veterinary nutritionist.
Yes, lactulose orally and an enema are all right. You will need to add in Denosyl and probably milk thistle.
Is this pup under the care of a board certified internal medicine specialist? No surgery would be done yet. She needs to be stabilized first.