My Dogs Having Problems Walking

My dog named Nohla which my sister named her from a character from the Lion King Movie when she was young is now having problems walking. Yes thats how old my dog is. The Lion King Disney Movie had just been released so thats what my sister named her. Shes 13 years old because I remember getting her in 1995 after my other dog had gotten hit by a car and had to be put to sleep. Were thinking about getting her some liquid arthritis we have seen advertised on tv. Does anybody know if that medicine is any good? We are having to carry her outside for her to relieve her self because she can't walk out there. Shes a good dog and she gets tired of all the cats we have around. We have 5 cats and she does not have a doggy friend. Its no big deal when she sees another cat. She only seems to like one of the cats we have named trouble. Hes the only black cat we have and think thats the only cat thats never attacked my dog. All the other animals play fight with her sometimes which she gets annoyed by. So I guess thats why she likes trouble. Shes had about 3 surgeries since we have had her. She having bladder problems as well so we don't know if she needs another surgury or not. We really don't want to have her put to sleep because shes just part of the family and has been with us for 13 years. She always there to be my friend if I need her.