rescued 6 yo bichon poodle mix

Question
my dog was rescued from a puppy mill.  Female, a bit fearful.  She has not responded to "come" command.  After a month, she is just starting to take food from my hand, tentatively and not consistently.  When I tell her to "sit", she only does so after walking to certain spots, then gives a full belly up display.  She is improving with leash walking.  I want to add the "come" command for safety reasons and to be able to let her off the leash to run at times so she can have more exercise.  How would you suggest proceeding?

Answer
Start with her on a long lead, like a string tied to her collar, something lightweight. Call her to come and give her just a bit of pressure. When she takes a step forward toss her a great treat and give her gentle praise, but don't move otherwise. Then call her to come again and give her a treat when she comes a little closer. In subsequent practices withhold the treat till she's taken several steps working up to actually coming all the way to you.

Working with a group of people, or at least one other person, put her on the leash. Everyone gets a handful of treats. One person has ahold of her leash and the other calls her to come. The person with the leash then hurries happily and excitedly over to the caller, bringing the dog along on the leash. The caller then gives the dog a treat and takes the leash and then the next person calls the dog. Continue playing this game for about 20 minutes a day gradually extending the distance and having some people move out of the room. When she's got the idea and seems to be showing some enthousiasm, you can practice with her off the leash too.

Never ever call her when you can't make her come. She needs to know that "come" means: if I run over there and sit down, something great will happen and I haven't got a choice anyway so I may as well. If you think there's any chance she won't come, use a different word or just go get her.