Might be a little early but could she be about to come into season for the first time? I have read lots of posts on here regarding behaviour changes around their season. With Bonnie, she suddenly started barking a lot....we couldn't work out why because she's never been a barker. A week or so later, her season started.
Of course, it could just be adolescence, as JennyBee said. Oh the joys of our beautiful Cocker's
