Don't waste money on joint supplements, it's too late in her life for that, put cod liver or linseed oil into her feed, it will ease the stiffness after a few weeks of getting into her system (same time as a joint supplement would), but the cod liver/linseed oils are much cheaper and will do as much good as an expensive supplement at her age.
Might be worth chatting to your vet about a daily dosage of 'bute'. If you don't want to give her bute in feed, mix the bute in with a tub of strawberry yogert and syringe it orally, she'll soon look forward to it!
Best of luck with her.
GO