Ledda's in the Philippines mostly come from Balaoan, La Union. That is the seat of our family. Coincidentally, my grandmother's name was Adela Lopez Ledda. in the Philippines, this means that her maiden name was Lopez and her married name was Ledda. In the case of your grandmother, unless she was previously married and widowed before she married your grandfather, Lopez would have been her mother's maiden name and Ledda would have been her father's surname. There is a famous Filipino POW/veteran named Daniel Laureta Ledda who was the first Filipino-American to reach the level of colonel in the American Army. He, too, was born in Balaoan, La Union, and died in Sacramento, CA. http://cgmedal4-bataanpow.tripod.com/id11.html
Hope this helps in your quest.