Good Morning Sue and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
It is not unusual in older dogs, Sue, for their digestive tract to not be as competent as when they are younger which would account for the change in eating habits and stool changes. It is also not unusual for older dogs like Molly to have arthritis that is starting to interfere with the nerve supply that will cause pain that is showing as this panting and difficulty climbing stairs.
I would recommend that you give Molly a daily supplement of Glucosamine/Chondroitin available at the pet store and give her aspirin at 5 mg per pound every 12 hrs to decrease any inflammation that may be causing this interference with teh nerve supply to her legs.
Change her food, Sue, to a senior dog food for dogs with a sensitive stomach. This is available at the pet store as Royal canin or Science Diet.
If this does not help, have your vet examien Molly and run blood work to determine if there may be a metabolic issue causing these changes in her patterns.
Does that make sense to you, Sue?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, XXXXX XXXXX