Large dog with joint problems

Question
I have a large dog(about 90 pounds)who is a German Shepard, Pitbull and Chow mix.  She's about 8 years old and she has recently started having a hard time walking on her back legs.  She'll often be walking and then fall for what seems to be no reason.  I know she is over weight and that probably is some of the problem but at this point I don't know how to start helping her lose weight because she can't really run much and I have 2 other dogs who aren't over weight and we leave the food and water out for all 3 of them.  Is there a surgery that I can get for her to fix this problem?  When I seen the vet about this all they wanted me to do was buy tons of stuff that I couldn't afford.  I have heard of other vets telling people they can give their dogs baby tylenol for stuff like this but for some reason mine said no, it had to be the stuff they sold.  Any suggestions for this I can do to help her?

Answer
Angie,
You already know that you must change your feeding routine on all of your dogs in order to help the older one. If you can't even  do that, then how do you expect anyone to help you. I know that that sounds harsh, but it is what it is, sorry.

The food that you are feeding will also make a huge difference. If you put her on a quality, grain free food (not one of the high protein ones)you will find that she will improve and also loose weight more easily. If you can find Canidae's Grain Free Salmon or Grain Free ALS, give one of them a try. All of your dogs would benefit greatly and in the long run, a better food will save you money because you feed less and you will save on vet bills.

There are several good supplements that you can choose from to help as well.  One is called DGP and another great one is Herbsmith's joint formula.

Change the food and drop her weight first and you may not have to get a supplement until she gets older.

I figure that this isn't the quick fix answer you were looking for, but it's the right one.