Philomena had originally left for her personal mission in the cloak of Masters herself. They protect from darkness even when traversing in between worlds, they hide one’s identity, and provide proper camouflage---at least in shadow.
But as the days passed after the fall of Radiant Garden, as Nobodies and Heartless began plaguing a world that had already long ago begun its fall, even with all Philomena’s insistence on tradition and rules, she began missing exhibiting her own light in all the darkness. She no longer wished to obscure her face and body in the harsh, dark leather that had now been claimed by enemies (mere children, still they had taken so many of her friends, her family). Still, in all her mourning and all her planning, she hid in plain sight.
Philomena was not surprised when no one recognized her, despite her telling them her name. No one noticed a strange sword if wielded by a woman who was willing to save you and your family from the Heartless. (Beasts. She hated them and everything they represented.) Not when Philomena left worlds almost as soon as she had entered them, researching, watching, collecting, fighting, with not a breath and hardly a word in between besides playful, un-reciprocated banter with Major Heartless.
She could have continued like this forever, perhaps. Merely trying to save Xehanort her boy from the man she had pushed him into becoming. Her fault.
But she had had more than one forgotten, abandoned child.
She had thought Kairi died. For a moment, after being told Kairi was alive, when Philomena had heard her own daughter had discovered the power of the Keyblade within herself, she had felt some small, blissful measure of pride before she felt self-pity.
Determination ripped through her as it always did, with enthusiasm abound. She had been a silent player in this war for too long. She had lost too many children to abandon her daughter again.
“I’m sure you’re wondering who I am,” she smiles. She had made Yen Sid arrange their meeting. Even an absent Mother can accomplish much when she sets her mind to it, with the right amount of nagging and wagging fingers. “I know Siddy wouldn’t have told you. He’s... not good with emotions. I hope he hasn’t been too rough on you.”
“If he has, I... I will give him a stern talking to!”
Despite her initial vigor when ordering Yen Sid to arrange their meeting, she feels herself quickly losing steam. She’s practically making small talk! She wonders, perhaps, if this meeting would be easier if she could hide her face.