How long does the dog have left?

my dog is a 14 year old english sheepdog/wheaten terrier. she isnt trained one bit(thanks to gramma) but ive come to appreciate she is cute and she does like being petted if you do it right. But ive noticed she seems to be having arthritis. whenevr she gets off the couch its really slow and it looks like shes in pain. she also does this when going up the steps, really slow and rather jerky, looks like its torturing her. Ive asked gramma countless times to get her some arthritis pills or see if shes in serious pain(if she is i beleive she shouldnt have to suffer) but she yells at me every time i bring it up. how long does she have left? btw thanks to gramma she isnt active and physichally fit. She isnt obese but she is a little overweight.