Thank you for your question. My name is***** I have been a small animal veterinarian for 13 years and I'd like to help with your question.
Dogs with tracheal collapse can be very difficult because they are often healthy in every other way. They just can't breath normally or without coughing. The problem is that not being able to breath well is distressing. There is no one right answer to your questions, but there are a few factors to consider.
First, I would make sure that you have done all that you can to help with medications. Is she on some kind of cough suppressant (such as hydrocodone) and some kind of anti inflammatory (such as prednisone)? If she is on these medications at appropriate doses, but her condition is not controlled then you have to evaluate a few quality of life factors. For example, can she eat and drink without coughing/choking. And, dose she sleep comfortably or dose she wake up constantly coughing. And third, is she able to get up, go outside, and interact with you without becoming distressed with her breathing. If she can't do these simple things then I would say that her quality of life is poor and it is time to consider euthanasia.
If she does well most the time and only has a problem when she is very excited then I would say she has a bit more time.
I hope that helps, but if you have additional questions please let me know. Please don't forget to rate my answer when all your questions have been answered.