As dogs get older, mobility becomes an issue. The hips start to go, muscles weaken, etc. It sounds to me like the kitchen floor is slippery enough she may have done a spread eagle and now feels safer going backwards. Try putting down some throw rugs and see if she goes forward on those. Our 14 year old Lab has mobility issues (especially getting up) so I have throw rugs throughout the kitchen. Once those went down, she started coming back in the kitchen which is where the water and door to the outside are so coming in the kitchen was a necessity. You may also want to ask the vet about a low dose of pain meds, too.