Should this dog be put down?

She's a teacup yorkie and teacups are just the product of 2 runts so they have bad genes. She is 14 years old, and has arthritis in her back legs, her knee joints pop out of place everytime she steps, and she can't even get on the couch by herself anymore. She has coughing spasms, her breath smells sooooo bad and she doesn't bark as much as she used too. I don't want to kill an innocent little dog and she's probably never gonna be put down even if she really needs it. (not mine, it's my moms dog and she gets a little too attached too things. You know unless it's my kinder dilploma then she just throws it away! [*****] anyway... Please let me know what you think)