I could see her being a little scolding. It's just basic consideration. When I forget to leave a note (or otherwise inform her) it's what they call "being inconsiderate". I try to leave a note or bring the cell phone with me. A cell phone means you're never out of nagging range...except maybe in Montana.
But if she is
really pissed it's because your little adventure demonstrates that she has not properly broken your spirit.
Bad dog! bad dog!
-Chris