I just finished watching part two for the third time (i know
) I think RTD left a pretty big hint as to who the Woman in White is... After Wilf asks the Doctor who she is, the camera focuses on Donna in the back ground and The Doctor just leaves it unsaid.
I take this to mean that after Donna dies a natural human death she prolly regenerates into a time lord and she regains her memories...
Per the woman in white being the Doctor's mother... the eighth Doctor said he was half human on his mother's side... You put two and two together and you can see why Donna may have been repulsed by people thinking she was the Doc's squeeze.