If she has any specific preferences regarding the envelope, she will generally include that information on her site.  I she doesn't, you can always ask her.  In general, there are 2 ways to go about it.  A) Put the envelope in a visible place where she can see it and go wash your hands, or B) wash your hands and leave the envelope in the bathroom.  Don't write anything on the envelope.  I should also mention that not everyone insists on an envelope.  As I said, check her website for clues.

It adds a nice touch as a book marker sticking out of an upscale magazine!

It is an old & obsolete concept.  Hpowever, there may be more at play here if she asks to do so:  if you can not follow simple instructions, will she trust you when her safety is on the line.  

If her site does not mention an envolupe, I don't use one.  However the corrdcdt donation should be carefully counted & kept together to avoid errors.  I use a big paper clip.