Not only does this get your dog the exercise she needs, but your signal to her when you carry her is that she's in danger. It's scary to put your little dog on the ground of this big world, but remember that you're adding to the fearful quality of her life when you hold her. Soon you'll notice that she acts more confident when she's walking than when she's being carried. She'll learn she's a real dog and can have a real life. Of course, use good sense with a small dog.
Little dogs are in real danger from attacks and even overly enthusiastic play from a large dog.
If a situation puts your dog in danger, of course you should carry her. One breach of trust, and we'd have to start all over. It's your job as your dog's protector to decide if the situation puts your dog in real danger. If the situation is safe but the dog is nervous, let her learn to walk on her own four feet. Early Nervous dogs take longer than more confident dogs to relax in a new situation.