Although the only person who can really make the decision to euthanize your pet is you, I think the biggest thing you can factor in is quality of life. If your pup is in pain that you cannot control or alleviate, if your pup no longer does any of the things she likes to do, then that is the point in time where you must consider that not forcing the animal to linger on is a kinder choice.
I think that it comes down to is trying to put the dog's comfort above your own pain of loss.
At some point you may find the website http://www.petloss.com/ and the rainbow bridge story some comfort. Hardest thing in the world about pets is that no matter how long they live its really never long enough, but making this decision for your beloved pet is the ultimate act of kindness...to end their suffering in spite of the pain and hurt it will cause you to lose her.
Hope this helps you!
Why is it so hard to read dogs? I so wish she could communicate with me.
Dogs are a stoic lot...and some breeds are more prone to hiding what they're feeling than others.
Both Mastiffs and Pitbulls were originally bred to be warriors...because of the kind of battle they were doing, showing any sign of weakness (such as pain) would have been viewed as a reason to attack them more...sort of like lions picking the weakest member of a antelope heard to track, hunt and kill.