Lucy Dachshunds probable cause(s) of death

Question
My 12.5 yrs. old overweight red spayed female dachshund died on Dec. 26th.  I am trying to determine or make an educated guess about the cause.  In Oct. the vet put her on Hill's R/D which she ate with no problem.  During the last two weeks of her life she didn't want it.  She would gobble down regular kibble or table food.  She had developed mild ventral itching several months ago which responded to belly washes every few days. Friday evening, 12/17, the itching worsened and was barely responding to bathing and topical applications.  I'd rub her chest and belly and she'd drop off to sleep.  I took her to the vet Monday morning, 12/19.  She now had extensive reddening over her entire ventral area and between her digits.  No pustules.  He thought it was contact dermatitis.  She was exposed to nothing new inside or outside.  He gave her cortisone based topical spray and other topicals which quickly cleared up all the redness and itching.  On Friday she developed pain and abduction of her left hind leg.  The only trauma was that morning when our Australian Shepherd clipped her as they were going out the door.  She never yelped.  The vet xrayed and found no fx or dislocation.  She had a slight temp elevation but WNL. He removed two large skin tags from her left thigh.  She recovered from general anaesthesia and was acting normally, alert and walking.  Over the weekend she hardly touched her water, wet her bed, would eat only table food or treats, and grew more and more lethargic.  She lost her fiestiness and was quite content to let me do whatever I wanted.  She always slept a  lot but now she was sleeping in odd positions.  She was responsive but lethargic.  She had another vet appointment on Tuesday, 12/27.  When she was up and walking on the 26th she kept her tail tucked.  She always held her tail up and was fearless.  The evening of the 26th she was lying down, sleeping.  She yelped and I picked her up.  I thought she was lying on her sore hip.  I held her in my arms, she looked at me, then her neck went limp, she paddled her feet vigorously, took three long, difficult breaths, voided and defecated, and it was over within minutes.  She had a pulmonary valve murmur, glaucoma in her left eye, was s/p stroke of several years ago, had long term darkening of her abdominal skin and urge incontinence.  I believe she had started the dying process around the 17th and was going through it during the week.  I just missed it.  I asked the vet when we were there if the redness could be liver or kidney but he said not kidney, and icterus would precede a rash caused by liver disease.  Do you have any thoughts on what caused her death?

Answer
I am so sorry for your loss.  I had issues with my old dachshund in November.  He had a heart attack and had problems with lethargic, paddling, defecation, excessive water buildup, etc.  but I had the misfortune of having him mis-diagnosed.  I took him to a different clinic and got the right diagnosis but he died the next day.  I really cannot give an opinion as I do not know her, sorry but I am not a vet.  At her age, I am suprised she went under anaesthesia for skin tags, but again, I was not there and do not know if they were a physical issue for her.  My old man lasted a week and I had a chance to spend his last day with him even though I wish he were still here.  It is hard to cope with, but remember the good times and the happy life she had.