i think you maybe have to talk to copycat or what she is named. then she mention the lost item which maybe triggers the lost-item-event so that you can get the pokedoll thingy ?
I dont remember so good about that since it is a long time since i played that part. but try that maybe
I'm guessing you never played RBY or FRLG. She's in one of the houses in Saffron; I think her house is next to the fan club or something (it's in the northwestern part of town). As for Latios, it depends on your version. If you have SS, he'll start roaming after you do the thing with Copycat. If you have HG, however, you'll need the Enigma Crystal event item. More info here.
EDIT: Not next to the fan club, but still in the northwestern part of town. To get the Lost Item, you have to go to the Vermillion Fan Club, then return that item to her, I think. Once you have the item, Latios will start roaming (or Latias in HG).