
As she is fine when she sees you, maybe she is going a bit deaf. Why don't you try a whistle, one of the acme dog whistles have a high pitched tone and should get her attention. You will have to do a bit of training with it first so that she knows what you want.
Alternatively try playing ball with her while you are out, this will keep her attention on you and hopefully not go wondering off.
Good Luck
Sandra