I have seen small breed dogs with hip problems, even at a young age. So the simple answer is yes you should be worried and you should have your vet assess your dog. Now understand that the smaller the dog, the easier it is to falsely think they are walking stiff so dont be surprised if your vet finds nothing wrong.
Other then hip dysplasia, this could be a problem with one or both of the knees (patellar luxation especially), or a condition called OCD.
As a practicing veterinarian and former Pomeranian breeder, I would talk to your vet about this and be sure to check the stability of her hind leg knees which in dogs are referred to as stifle joints.
Weakness of the tendons and/or ligaments in these joints is the most common musculoskeletal injury in dogs in the USA and its very common in Pomeranians.
I hope this is somewhat helpful
Dr Carol Osborne, DVM