I would say that your first step would be to have a vet trusted come out and do an exam. It's not always easy to tell exactly what is wrong with our horses--sometimes we think its one thing but it could be another (same with us!). I have found that it is best to get a professional opinion and follow that with well-educated advice before making our own changes.
From my view, the problem does sound joint related and I have been recommended by my vet to use to Smartflex Senior from Smartpak (my horse has various joint problems)...it has high levels of glucosamine, chondroitin, hyaluronic acid, and msm as well as amino acids and herbs like devils claw which has a similar effect like bute with way less side effects. It's a very well-rounded supplement. I have heard that oral liquid hyaluronic acid is beneficial and there are also joint injections that can be administered by a professional as well as other injectable possibilities..
At this point, if it is just arthritis, barefoot *tends to be the better option over shoes. However, you might find out that she has an issue that would benefit from particular shoes. 24/7 turnout (minus the occasional in-day or being brought in for grain and turned out) is the absolute best natural and non-invasive thing that you can do for a horse with arthritis! Being left in at night, even if out for the day, can really cause a horse to stay stiff. Movement like turn-out and regular exercise is essential to keep the joint liquid flowing. Even if you take her on trail rides and go over basic flatwork just to keep her moving, that is helpful for her. Make sure she has really well trimmed and balanced feet--whether you go for the shoes or not.
Good luck :)