Your lips turning blue may be a sign that you're not getting enough oxygen in your blood, which would make sense if you have asthma that isn't under control (you'll see the same thing in your nail beds...they may look a little bluish, as well).  I would suspect that the doctor ran the EKG to make sure that there wasn't a problem with your heart that was causing low oxygen in your blood.  Given that the EKG was normal, it sounds like the doctor was thinking that your blue lips were a result of your asthma being out of control.

The prednisone she prescribed will help to quiet down the inflammation in your lungs - and depending on the medications you're using in your nebulizer, doing your neb treatments will both open the airways in your lungs, and work to reduce the mucus in your lungs caused by the inflammation.  Treating both of those things (opening the narrowed breathing passages and decreasing the mucus caused by the inflammation) will help the oxygen you're breathing from the air get from your lungs into your blood stream.

My 24 year old son recently had a serious asthma attack and ended up in the ER.  The ER doc gave him this little plastic hand-held device called a peak flow meter.  He showed him how to use it - and told him what to do depending on what the readings were when he used it.  Above a certain number, everything was fine.  Between 2 other numbers, he needed to be using his rescue inhaler.  And below a certain number, he needed to get to the ER for more intensive treatment.  With this kind of self monitoring, the idea was that he could initiate treatment himself - and hopefully avoid the kind of crisis that put him in the ER in the first place.

Talk with your doctor about whether you're a candidate for using a peak flow meter to do this kind of monitoring from home yourself.  If your doctor's office doesn't stock them, then your doctor should be able to write a prescription for you to pick up one at the pharmacy. (a doctor's practice I ran several years ago used to sell them at cost, which at that time was about $15).

Also, I don't know if your doctor is a primary care physician (internal medicine or family practice) or whether she's a pulmonologist (lung specialist).  If your asthma isn't well controlled and you haven't seen a pulmonologist yet, it might be worth your while to see if this lung specialist might be able to adjust the treatment regimen you're on so that your asthma is better controlled (if the treatment regimen your current doctor has you on isn't the optimal one, that is).

Good luck!