Undecided Question

Should I have my dog euthanized and how should I handle the situation?

My mom passed away in october and she left our 14 year old shih tzu for me to take care of. Lately all the dog does is sleep and barely moves. when i let her outside she never seems to move, even when i call her to come in. She disobeys and never has before. She started urinating and pooping in the house which she hasn't done since she was a puppy. She hardly eats but still drinks water. She is blind, and i think she is becoming deaf and losing her nerve system. She crawled under the wood stove and it burned her hair and skin, but she didn't notice. She weezes and sometimes acts as if she has dementia. I love my dog very much and i am afraid to let her go seeing as she was my mom's dog and has been in my life since kindergarten. I don't know what I should do…