(seemingly) random aggressive behavior!

Hi all :)

This is my first time here so be gentle :p

Anyways, my parents (I'm 22 and come over to visit every so often, so I'm not in the home all the time to see every ounce of behavior) own a 3 year old Goldendoodle named Abby (and they've had her since she was a puppy). She started off fine, but after some time my parents went on vacation and boarded her, and since then she's been completely different (this vacation/boarding was 1.5-2 years ago, so it happened early on).

The problem has become increasingly worse, as it started out not too noticeable though now it's blatantly obvious. She is VERY possessive of her treats/toys. She'll growl, bark, and snap at you if you get near. Other times, she will be laying docilely on the couch, getting a nice pet, and she will begin to growl out of no where, and hop down and move to another place. Another odd behavior is that she'll pick up a toy and bring it to you (she loves to play fetch), but when you go to grab it from her mouth, she growls and turns her head (almost as if she's playing some kind of game with us!)

None of this behavior is 24/7 constant, it just happens at random intervals throughout the day. My dad has owned dogs since he was a child and has never had a problem being the "alpha", and she listens to him just fine, so I don't think it's a leadership issue....I just don't know what it is!

Any help, suggestions, links to look at, etc would be greatly appreciated! Sorry for such a long post, but her behavior is getting to the point that at times it feels unmanageable. My parents have worked with several trainers/obedience classes trying to correct whatever is wrong, and nothing works :(