I'm sorry to hear that. The condition will probably not heal itself spontaneously, as it is caused by with nerve, muscle, or anatomic damage. Latest treatments for footdrop include stimulation of the peroneal nerve that lifts the foot when you step and braces like The Soft Foot Drop Brace. But the treatment for foot drop will depend upon the cause --- do you know exactly what is causing your sister to walk like this?

They told her that the surgery, which was supposed to have lasted about 2 hours, went on for 4 hours, due to all of the scar tissue (from previous auto accident.) They said that they had possibly left the tourniquet on for too long and damaged the Peronial Nerve.
I'm wondering how much improvement might there be, once the swelling from the surgery goes down? It has been nearly a week since her surgery, and she is home now. They fitted her w/ some sort of brace. Her PT has been slower than originally planned b/c of the footdrop complication, but she reports that it is going better now than before. She has been experienceing some pain in the Tibialis Anterior, which sounds like a good thing to me- in that I should think that indicates some neurological activity. I'd appreciate any info, as her doctor has really not been forthcoming with information.
Is there anything that she ought to know at this point in time, that might influence her recovery? (Like, are there any particular therapies, etc that need to be started sooner, rather than later?)

For Peroneal nerve damage, neuromuscular stimulation and FES are referred to as potential treatment options. I also want to let you know that I'm not speaking from personal experience, but this information is based on some preliminary online research. I'll be happy to help you.