If it has been going on for more than 72 hours I would go to the vet.
She may have a virus or something. She may be dehydrated due to the diahrrea.
Is she on medication for the arthritis? Some meds can cause gastrointestinal distress.
If that’s the case the vet may need to change the med.
Good luck and give us an update.
PS:You could try boiled chicken and white rice for 3 days, but it sounds like this has been going on for a while, so I would go to the vet first, he may want to run some tests.
Has she had a senior workup, labs, dental check within the last year?
If not she is overdue.
Seniors are vulnerable, some pet owners take their senior dogs to the vet for a checkup every 6 months.
