Hi Lorraine, I was surfing and accidentally viewed your message... Its been months since you posted this message hope you heard something good already about your aunt Deding. Anyway, Arellano clan in the Philippines is so diversified we have actually relatives all over parts of the country from Northern Luzon down South in Mindanao (which I just learned very recently).
Bulk of the clan though is in Luzon, Ilocos region particularly in Tarlac, where I grew up. And there are also many Arellano's in Manila and Cebu.
If you have any idea which province/part of the country your Aunt Deding may be staying, then I can probably help you out.