Laila is Nanael's assistant. She was living on the terran world before the Head Angel found her. She was taken to the celestial world and became an angel trainee under Nanael’s supervision (much to the despair of those around). Nanael, who went on rampage, ordered Laila to clean the chaos on the terran world with the “Divine Punishment” using holy milk.

(Source: Queen's Blade Wikia)