Advice on when the time is right

This is my first post ever and I hope that shows how desperate I am for some kind of support on this. I have a 13 year old (F) basset hound who has been in my family since her first few weeks of life. Shes the best dog I ever could have asked for. My parents insist on putting her down this next week and im having a hard time coming to terms with the idea that im not ending her life prematurely. She has struggled with osteosarcoma for five years (I know thats crazy and we’ve had her checked by many vets who confirmed the diagnosis) and its now progressed to a giant (about the size of a baseball) ulcerated MCT under her arm. Its stinks to high heaven, bleeds, oozes and it requires constant cleaning and care. Shes been living in a sling to keep her from gnawing at it. I have to change her pillows and blankets every week at this point because the whole house reeks.

Other than her tumor, she coughs and wheezes, her poor legs give out on her and she tends to have #2 accidents at night. We think she may be in the early stages of doggy dementia as well. Despite all this, she acts excited and happy to see us, eats and drinks normally and loves her treats. She gets up the stairs decently well and her coat/nails are very well maintained by me. She still plays every now and then too.

Im mainly the only one in my family that manages her care on a daily basis and im moving states in a month. I cant stand the thought of her declining because im gone. Im at a loss. I need reassurance this is the right course of action for her. I don’t want to throw away extra time i could have with my sweet girl.

Ive put so many years into her utmost care making sure I could have her as long as possible with her cancer diagnosis. PT, homemade raw dinners, grooming her myself, medication, frequent vet visits, her wound care daily ect has been my whole life it feels like. Taking care of her has been a full time job. But Im not sure im ready to throw in the towel yet. Any advice is greatly supported yall.