Is Bertie just not a great dog or are you not really an animal person? Seems like you have some real antipathy toward that dog.
I love animals, the sole exception being dogs.
Cats, snakes, hamsters, rats, guinea pigs, birds, lizards and so on I would gladly take care of with no complaints. Hell, I even used to feel more than a bit of fondness towards the roaches I kept as animal food (for my lizard, who was a bitey and flighty asshole, but I loved him.) I'd cheerfully babysit a crocodile provided it was still small enough to care for single handedly, or spend a week caring for a donkey even if it was an asshole.
Dogs, I just cannot stand, never been able to. Was getting better at tolerating them through spending small amounts of time with some geriatric small dogs, but being forced to be around Bertie has actually undone a lot of that slowly built up tolerance because he engages in almost every behaviour that makes me not like dogs.
Regarding the dog particularly: If you are inclined to feed the dog, provide it water, and not hurt it... you're a better dog owner than some people. Eh, taking care of things is emotionally healthy for a person, even if a chore.
Also: Sounds to me like your mother is cheap. Try asking for money to take care of the dog. She'll either change the subject or you might find it more palatable with some financial reward attached.
I would most likely forget to feed or water Bertie fairly often, and would essentially wind up emotionally neglecting him. My usual response to having to be in the same building as him is to shut the door and ignore his existence.
I'm also pretty much entirely unmotivated by money, if I don't like doing something then money isn't going to make it more palatable, but I'll happily do actual work I enjoy for free. Hell, I used to spend money on bus fare and lunch so I could help out at the local pet store for free just because I liked working with the animals and customers.