Glucosimine is a good option. You can get the kind that you sprinkle on food or there are chew treats. Here’s a web site that helps you figure out which is right for your

Feeding a speices appropriate diet, is your best bet. keeping her active and at a healthy weight, while feeding her an appropriate diet so she has a strong healthy immune system. Swimming and walking are the best exercises you can offer her, so you are off to a great start!
here are some links on feeding

Also limiting her vaccines with the theory “less is more”. This will help prevent vaccinosis which can manifest itself in arthritic conditions. Heres info on that

You can feed shark cartiledge and a gluc/chondroit supplement both of which can be found here

Another great supplement can be found in Nzymes, more info on them here

Hope this helps

This answer might seem a bit off the wall…

Try feeding your dog one can of sardines a day. If she’ll eat it - it may be the solution. There is a dog food which contains fish but if it is salmon it has to be wild salmon to work. The reason is that ONLY fish from the ocean contains the 72 trace elements needed to work. [Not to mention that farm raised salmon is high in toxins.]

This is why shark cartilage might work but I think that the whole food would be best. Seafood from larger fish like tuna and shark are much more heavily tainted with mercury.

Reference the web site below to see why I suggest this.