Animal urin is the worst kind to deal with. The machines will always smell and get condemned for the rest of their life by the manufacturer and any good tech. On top of that, the manufacturer WILL void the warranty. Apple already considers secondhand smoke systems a biohazard so I presume any type of urin counts as well. If I get to take it and it's worth stripping I'll wear gloves and take what I can out but I do not keep much; I will even throw out the chassis. I do not repair them for anyone, including family.
Your friend should just go for data and replace the machine; it's probably not going to last very long knowing it was used as the dog's bathroom. Get it repaired so it's stable enough to move the data to an external drive of some sort and erase the SSD once everything they need is off. This will certainly involve board level repair, so find a schematic for the board to use as a reference. Once you do that the board needs to be cleaned with a ultrasonic cleaner to make sure all of the urin is cleaned off.