Pred is a wonderful and hateful drug combined. It offers rapid relief from severe symptoms and provides a "euphoria" for a while.It also causes at doses at/higher than 7.5mg a day adrenal atrophy,bone loss,weight issue,stretch marks,easy bruising and further lowering of the immune system.
Every dr is different and a higher dose of prednisone is used when issues "flare up" or you become ill.Being on a higher dose will not alleviate the achy,tired or run down feeling IMHO as that is likely the SLE. If you feel like you are having better days then have an honest talk w/your dr and see if they feel it is appropriate(via symptoms and labs)to up the dose. I would not change a dr I was having no issue with to go to one simply for a higher pred dose honestly. Your friend may dose higher as her dr feels it is appropriate for her.
The goal of pred is not to be on it forever as it is destructive. I have been on it since diagnosis while trying to find a medication to calm things down. I have done Imuran,Arava and am currently on MTX. I am barely over 40 and have been on an osteo med for 3 yrs to prevent bone loss because I haven't been able to drop lower than 7.5.
Even if you go up,when you come down you will have prednisone withdrawal which is like the flu really(for me)and all the symptoms return. Plus you run the added risk of additonal infection and urgent care or hospitals treat you like the plague if you have to go and they see those meds. I hate hospitals BTW .
So it is up to you really to talk to your dr about increasing. if you are noticing improvement with the Imuran I would give it more time. Just because your friend is higher and youre not doesnt mean anything-its not going to be a magic pill-there isn't one and fatigue, achiness, fevers,etc are a nature of this illness. I would consult with the dr at your next appt if you feel it would help and see what they say but generally they like to keep you as low as possible on this medication due to the severe side effects and damage it can cause. That is usually why they try to find a DMARD(disease modifying anti rheumatic drug)to use in conjunction (like Imuran) to spare using the pred. Unfortunately some of us just don't respond well enough on those or find the right one and the pred has to be continually used or often changed due to disease activity.