First let me say that is a beautiful shot and pretty close to perfect if perfection can be obtained.
I wanted to comment on your use of the bed sheet. While you say you don't need fancy light boxes and umbrellas you don't mention their advantage and their real value.
Using the bed sheet may work fine as a light modifier, which for those that don't know, difuses the light coming from the light source making it softer and more flattering on the subject. But what you don't mention is that to use the bed sheet you had to hang it on some sort of frame or rod so it's placed in between your model and the light source and to make it movable, so you could get it into the best position, you had to have it set on stands. By the time you have that all set up you pretty much have a home made light box.
While the end result is virtually the same, you get the extra manuverability and convience in a self contained light box as opposed to rigging up a sheet. Being resourceful is very important in photography and using a bed sheet is a great tip however givin all the other stuff you need to make the sheet work I don't see how it could even come close to functioning as well as a light box.
Also I'd like to add that in no way am I implying that all you have is a bed sheet to work with. My comments are directed to the beginning photographers and in the spirit of which this thread was intended.
Here's a shot I took with no light modifers, just backlite from the sun
