Reply #5: The oldest living dog is 27

[Lorien]

he's a border collie in England who has been fed a vegetarian diet for most of his life (according to Guinness).

Just keep her on the highest quality food you can find (no meal "meals" or corn products in the ingredients), and she may well live past 18. If the vet says she's healthy then take him/her at their word. It's sounds like you are an excellent "dog parent".

It's one of the cruelest facts of life that our fur children can't live as long as we do. Just treasure every day you have together. Healthy older pets generally just stop one day, so I wouldn't worry about helping her to leave this life unless your vet tells you that she's really suffering. If she's still having puppy moments, then it sounds like she's doing quite well.