Hi there,
It sounds like your girl is leading a double life. She may have another family that is feeding her. She goes there and stays awhile and then comes back to you.
This is actually quite common as cats are not usually loyal to one owner.
Try to follow her next time and see where she goes.
Best wishes to you,
Terri
Feline Healthcare Expert
Expert in feline health and behavior. 20 years experience with cats.