my aussie cattle dog mix just turned 2 and for a couple of weeks she has been stiff on her right back leg and will sometimes limp after a walk, theres times when she wont chase her ball.

we talked to the vet and he said he wasnt concerned but i think somethings wrong. we’re considering buying her some glucosamine tablets to help.

any suggestions?
she isnt over weight at all , very lean and not built like most cattle dogs, this is becuase she’s mixed with kelpie ,border collie and possibly fox terrier