@celia16 I have found from my own experience, that making sure my different specialists are in communication with each other, as having multiple health conditions going on can be quite a challenge! It is a balancing act, as I like to say. Making sure my diet is following different conditions/situations, medications take into account the different health concerns. For example, my treatment for multiple myeloma is tailored based on my kidney disease status, and those two doctors talk to each other frequently.

Being considered for a transplant, a transplant center will evaluate based on a patient's overall health, comorbidities [in your aunt's case, the lupus, plus anything else she has going on], the ability of the patient to take care of themselves after transplant, mental status, plus a lot more!
Age may or may not be a factor, as the posts above show, from @rickkaplowitz and @m1rmiller
Ginger