15 year old dog with kidney failure.

My dog Gyppie had a bloody stool, large. We took her to the vet. He ran blood work, did an ultrasound of her abdomen, x-rays, exam. He said she had kidney failure and would need IV fluids and then take meds twice a day for the rest of her life. He did not know what was causing the GI bleeding, stated her abdomen did not look good on ultrasound, and though she may also have lymphoma. This was a shock. He said if we treated her she may have 'several years' left. She seemed so healthy two days before. She had decreased appetite which we attributed to aging (in error probably) and changed her food until she ate again. She was 15 years and 5 months old. I have had bad experiences with promises and outcomes from two other vets, loosing two animals after they suffered through treatment, only to die soon thereafter. I did not want to see her suffer so I chose to bring her home and keep her comfortable until she passed. She died on Friday, Sept 20. Today is Monday, Sept 23, so I am still grieving and am questioning my decision in not treating her. Did I make the right decision? She ate one of my daughter's soiled feminine napkins - the ones with the product that turns into a gel when moist. Could this have been the cause of Gyppie's acute kidney failure? She was the puppy love of my life. I just need an honest opinion based on your expertise. I have read that rat terrier's life spans can be from 15-23 years. Did I deny her a longer, healthy life?