Murder her. Try to do it cleanly, leaving most of her skin in tact -- I suggest poisoning.
Once she's dead, make a very careful incision down her back, being sure not to make any unnecessary marks. After that, remove all of her organs, muscle, and bones (yes, that includes her brain, eyes, etc.!!)
From there, you should just have her skin. Then, you can slip it on like a suit. It should fit nicely, as rigor mortis results in increased flexibility of dermal tissue.
TADAH! You can now live life as your friend. No one will ever know the difference.
