Hello and Welcome to our family;
I applaud you for wanting to learn about this disease in order to help your wife. I agree with her, she should not let this diagnosis stop her from doing those things that she loves to do. Such as riding on the back of your motorcycle with you in her arms.
I would suggest a few precautions, however, so that she can enjoy this as much as possible. Please be aware that the sun (UV/UVA rays) are one of the worst enemies of Lupus Patients. So, we should try to avoid exposure as much as we can. I would suggest that your wife wear sunscreen (minimum 50 SPF) all over her entire body. Also, that she wear sunglasses that block UV/UVA rays and a hat. I don't know if you are she are wearing riding leathers or not, but in any case, she should wear clothing that protects her body from sun exposure. Perhaps you can limit the amount of hours that you are riding during the day. Take a lot of rest periods where she can sit and recuperate (make sure that she does not get overly fatigued) and keep her hydrated.
You mentioned that she is taking Xarelto. Does she have venous thrombosis? Is she on any other medications for her Lupus?
I am glad that you joined our family and please know that we are here to help you in any way that we can. I wish you and your wife many happy hours of the road!
Peace and Blessings
Look For The Good and Praise It!