Digging up old information from html websites, they do shed some light on what she said in one USATODAY interview. In some of those profiles, Britney Spears said that her favourite animal is puppy and she tends to like smaller dogs. It should be noted that in some of these sites, she had a Rottweiler though who knows if it was a puppy at the time.
And who knows if she got scared of dogs after buying two German Shepherds. A better question is if she had changed preferences or not. But it’s safe to say that while she didn’t exactly specify the timing, her preference for puppies (and smaller dogs) is related to her experience with getting bitten by other dogs.
It’s also safe to say when she photographed her son posing with a Retriever, she would have tolerated it and like any mother whose child is playing with a strange animal she would have allowed it for awhile. She also didn’t photograph herself posing with it so that clears things up.