Chronic disease disease is often painful, as is arthritis which she is sure to have at this age.
Incontinence is not typically painful, unless she is getting urine scald.
Arthritis is typically treated with dog safe NSAID medications such as rimadyl/carprofen, deramaxx, metacam/meloxicam, previcox, etc. They get a large amount of comfort from this. These are similar to human NSAIDs like ibuprofen, but much safer.
Incontinence can be treated with two different medications: Proin, a twice a day medication used long term; or DES (an estrogen) used weekly. The proin has less potential side effects (usually only upset tummy in a small number of dogs), so I usually start there.
Your vet can prescribe the pain medications and incontinence medications. I would start there. She will be so much more comfortable. If you feel she should be put to sleep that is your decision, however I would try these medications first if she was my dog to see if she moves around better, gets more energy, and seems more comfortable.