The flattening out is the snakes way of trying to scare a would be predator.
In all honesty when I said let the snake settle in, I meant that you should leave her alone for like a week, no handling, zero touching.
I know how difficult that may sound, I can tell by your posts that you are completely enthralled by your new friend.
Not that I want to discourage you or anything, but the pictures you posted of the snake perched on your guitar are constantly on my mind, It's easy to mistake a terrified animal with "calm"
Try and think of it from the snakes perspective, you just came out of a long winter hibernation and some giant creature just scoops you up from your natural habitat and bring you into this big giant place unlike anything you have ever seen, and then sits you on top of this giant thing that vibrates... (She has no clue what is going on, and therefore is frightened for her very life).....
Would you feel like eating?? probably not.
Another thing to take into very serious consideration is that if your snake is in fact a she, then she very well could be gravid (pregnant) and that concerns me as well.
I have been in this forum thing now for quite a few years, and have read many stories posted by nice people just like yourself who picked up a wild female snake only to wind up with a huge litter of babies, and in several of those cases the babies wound up dead for one reason or another.
You need to do some serious soul searching and decide if what you are doing is really in her best interest, I will gladly guide you along in whatever decision you make, just try and think of your little friend and what you really want for her.