Thank you for your question Hope's Mom. Sorry for the delay getting a response!
Arthritic changes in the knee, just like in many joints in the body are inevitable as we age. When we look specifically at the knee joint, it is particularly at risk for injury or degeneration simply because it lies between the hip and the foot. This means that any weakness or instability in either the foot or hip will increase the stress placed on the knee. This also means that one of the most effective techniques for preventing knee pain is through hip and foot exercises.
So what does this mean in your case?
I would integrate a program the integrates mobility & stability/strength.
Mobility: Make sure your calves (ankles) are flexible. Any calve tightness increases the stress (and ground reaction forces) placed on the knee joint. Make sure your hips are flexible - specifically your TFL (or ITB), hip flexors and adductors. MOST causes of knee pain in runners is due to a tight TFL (ITB) because 1. it is a hip flexor and 2. it specifically stabilizes the knee when your foot strikes the ground.
Stability: After you mobilize your ankles and hips, you want to ensure you have stability in the ankle, knee and hip. This means you will want to strengthen the foot (posterior tibialis muscle), knee (vastus medialis/VMO) and hip (glutes).
One of the best exercises for strengthening the foot, knee and hip simultaneously is balance training or single leg exercises! Of course you will want to do them barefoot
This is of course all said without knowing what your foot type is.....but this is a great place to start! If you do not have a severely over-pronated foot I would not do the cushion-sneaker/orthotic bit.
And as far as omega-3s - great idea!! I love natural anti-inflammatories. Another great one is
Bromelain (found in pineapples) and Quercetin. If you have any other questions - please let me know!