Sagging skin due to long-term prednisone use, what are my treatment options?

Make sure you coordinate care with you plastic surgeon and rheumatologist/immunologist. With your history, you have to be very upfront with your plastic surgeon and other MD's.
The biggest problem would be wound healing, especially since you have been on extended prednisone treatments for many years. This will "thin" the skin/dermis and decrease your normal wound healing. 
Start taking your homeopathic medicines, such as Vitamin C, pre-op Vitamedica and others that will help healing. Good luck! 

Prednisone is sometimes used for the treatment of chronic immunologic disorders. It can be very effective but also has some very bad side effects, especially to bones, skin and conective tissue. It basically decreases the body's normal construction of new collagen and other building blocks to support bone and skin. It also decreases the body's ability to fight infection. Surgery, including facelift surgery can safely be done in patients who have been on Prednisone in the past bas well as patients who need to continue taking Prenisone. It is important to tell your surgeon that you are taking Prednisone in order to prepare you properly both before and after the surgery. Good luck.

There are much better options for facial laxity for patients in their 30's than previous years.  Facetite (RF delivered underneath the skin) is an option, as is combination facial fillers and laser resurfacing.  Often times laxity can be a result of volume loss.  It is unusual for a patient in their early 30's to have a facelift.  Best Dr. Anil Shah