12 Year-old Jack Russell Has Become Aggressive, Her Teeth Have

12 year-old Jack Russell has become aggressive, her teeth have become loose and she limps..she also has collapsed and urinated on herself..several times over the past year and a half. Most times she is playful and normal, a sweet dog. But she does get aggressive at times with my other dog, so much so that they get into the zone of fighting and I fear for her life..she is the weaker the two, but has always been alpha. She does cough as if choking after a period of barking, or while on the leash. This weekend the fighting has occurred twice and was followed by the collapsing spell.