Rheumatoid Arthritis Support Group
Rheumatoid arthritis is a chronic, inflammatory, multisystem, autoimmune disorder. It is a disabling and painful condition which can lead to substantial loss of mobility due to pain and joint destruction. The disease is also systemic in that it often also affects many extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and...

Your Rheumatolagist should be able to tell you what severity he/she considers your RA and whether he considers it aggressive.
Cheers and hope this helps.
My doctor told me I was considered moderate to severe, then we discussed treatments.
I've also had appointments where my number indicated the medication was controlling the RA well but my body would disagree & vice versa.
Like with many medical conditions the tests may not always match what the patient feels.
I'll take pictures if there's a lot of swelling as I know it can change day to day.
Your half sister is lucky & I hope it remains so treatable for her. Then again RA can play a game of hide & seek. It can rear it's head in other ways & areas of the body not so visible.
Wishing you the best of luck.
Blessings
Sammy