Whats going to happen to my dog?

my dog, Cindy is a 14 year old wheaten terrier/english sheepdog. she eats, poops, and drinks fine but there's something wrong with her legs i think. she always struggles to get up in the morning, she sometimes will slip and fall and she cannot go up and down the stairs leading to the basement or kitchen, but when i let her in from the house through the basement door, there are stairs she must go down to reach it(only 3) and she reaches it fine. about same size as the other stairs.(there are six leading to the basment/kitchen depending on what room you're in.) i want to put her on some pain treatment for dogs or at least get her tested for arthritis but my gramma(who i live with) says no. i tried everything imaginable tryign to change her mind(she even cried when i brought it up one day) but its to no avail. i also live with grandpa but he has no say over anything. ever hear of those dominat marriages when one controls the other entirely? thats basically grandma and grandpa. how long does Cindy have left, should she be on a treatment, or should she see a vet?