The infection part is the most dangerous. Like lesli said, if it's not infected, the woman could try the "banding" method. It's often done on lamb tails or when castrating pigs, cows, or goats. The area banded will die and fall off. But if there's infection, the cat could get very sick and die without vet care.
The best option is with a vet - they'll put the cat under anestisia (spelling?), there would be no possible pain for the cat, and then there would be antibiotics after for any started or possible infection.
My suggestions for her to look for would be - if the skin is dry and black, it's probably just dead and banding might work - if it's oozing, hot, puss covered.... then it's infected. Also, if the cat seems generally ok (eating well, not apparently in pain) AND the tail is dry and black - I would say no infection. But if the cat seems a little under the weather, even if the tail is black and dry, there might be started infection anyway ..... even if it can't be seen.