My dog favors her right back leg when walking. Although she is young, I think it is arthritis. What else is it

She should have a vet visit, if at all possible.

If you give aspirin, it should be buffered, or enteric coated, as aspirin causes gastrointestinal bleeding and anemia.

You might also get her a good quality kibble formulated for bone and joint health. Solid Gold, Innova, Wysong all make kibbles for this. Your pet supply will have a good one on hand.

Give her a bed that keeps her hips warm. Those fleece lined snuggle beds are great for joint pains.

Go to the vet and be very careful with the aspirin. Dosage should be figured by weight (eg. infants tylenol) and can be very toxic to their liver if she gets too much.

Some dogs have hip problems a trip to the vet might be in order.

Her leg is getting cold on the floor... Put her in a padded basket and that should help keep it warm and help the blood flow. Heidi

she could also have a slight sprain. But, I definitely would take her to the vet.

what breed is she?

some breeds are susceptible to hip problems or growing pains, how old is she?