She's still very young and has more growing to do yet. Is she a show or working Cocker?
My FTCh bitch isn't tall but she is well constructed, solid and muscular with a broad chest and strong head and muzzle. There's a photo on the 'one photo' thread of her retrieving a really huge cock pheasant, it was bigger than her but she carried it back -still alive and moving - over 300 yards of plough. They're not meant to be big dogs but should be sturdy and strong. Really small framed dogs, especially those with small, narrow muzzles may have difficulty retrieving large game, but they can still hunt/flush.