If she is definitely not pregnant, then it is very likely a phantom pregnancy. This usually occurs about eight/nine weeks after being in season, when the body is convinced it is pregnant, so produces all the signs such as nesting, cuddling toys and taking them to her bed, being very protective of them, and even in some cases producing milk.
If she was in season eight/nine weeks ago, this is probably the reason. You can either take her to the vet and get a jab which will reduce the symptoms, or you can let her go through the natural process, and gradually take her 'babies' away when they would be ready to go (well a bit earlier actually, about four/five weeks instead of eight weeks). You can give her stuff to take her milk away, epsom salts will clear it up, but unless you had either had her jabbed or she is happy to let her babies go, then she will just produce more milk.
It is cruel and unnecessary to just take away any 'babies' if she actually thinks she has some. If it is just the milk, then try the epsom salts and see if it dries up naturally.