I am sorry to hear that Lacey is having some trouble and they you are worried that it is almost time to let her go. My name is ***** ***** I have been a veterinary nurse for 26 years. I would be happy to help.
Frontline has become ineffective for some dogs so we can not rule out fleas. Also if she happens to have a flea allergy all it takes is one flea to set off a reaction. Environmental and food allergies can also cause an itchy bottom. Lastly considering her age and the fact that she has fallen it could be that she is chewing due to pain.
I would start by trying something for allergies. You can try Benadryl or Zyrtec.
Benadryl is dosed at 1-2 mgs per pound of body weight 2-3 times per day
Zyrtec is dosed at 0.5mgs per pound of body weight every 12 hours.
If this does not help then you can try aspirin as long as she is not on any prescription medications. This can be used short term 3-5 days. Aspirin is dosed at 5mgs per pound of body weight every 12 hours. This can cause some digestive upset so give with food. If she has any vomiting or stops eating then I would stop using this. Use aspirin only no ibuprofen, naproxin etc.
I know making the decision to let go is never easy, unfortunately when their quality of life diminishes and they become painful or uncomfortable the last act of love and kindness we can show them is to let them go peacefully with the help f your vet.
Hopefully the above suggestions will help make her more comfortable. Please reply back if you have additional questions and I will be happy to continue. If your questions have been answered please take a few moments to provide a rating so that I am compensated by just answer for assisting you today