I don,t suppose it could be something as boringly simple like she simply fancied a new hair cut? Why does it have to mean anything else?
Achem's Razor at its finest: All things being equal, the most simple explanation is probably the correct explanation.
I think she just felt like cutting her hair shorter. Did that recently, myself. Something I've wanted to do for a long time, and the spirit just moved me one day, so I said to my hair stylist, "Go for it."
If it has to mean anything at all, it means she's secure enough in herself and in her relationship that she knows making a change like that won't hurt a thing.
(Sorry to be so late to the haircut party, by the way.)