Didn't mean to start any drama...
My understanding is that if a woman was adopted (let's say the adoptive mother is an AEPhi, for simplicity's sake) the chapter is not, strictly speaking, obligated to treat her as a legacy. However, I suspect that most chapters would treat her as a legacy anyway, especially if the AEPhi is the only mother this girl has ever known. I would frown on any chapter that did not. It is (as with any legacy relationship) a matter of courtesy to the AEPhi.