Notorious "BUG"

Our 13 year old dog has a spot on her leg that we thought was a calous at first. It has gotten larger and bleeds quite often. She licks it and chews at it and in researching similar things on the internet it appears that she may have cancer. We suspected this a while ago but because she had no external symptoms we hoped for the best. She is very old and has had a very long and happy life. We are trying to decide whether to take her in to the vet and have her put down or whether to try to manage her pain (if there is any, she seems comfortable) and let her die at home. I would prefer to have her home when it happens. I used to laugh at people who were so attached to their pets but now I know what they were talking about, she is part of our family and it's hard to watch her get older and slip away.