Well, this is my first time answering a question, but I consider myself knowledgeable on Nasu lore so here I go!
First, an excerpt of her in-universe Profile:
Independent Manifestation: The ability to manifest independently in the world without a Master. This allows her to summon herself to the Indian Ocean, which she overtook in a mere seven days and allowed her to birth an infinite number of demons and monsters to attack humanity. In addition, she exists across all of space-time and is immune to time paradoxes as well as instant death attacks. However, since the ocean is her body, she cannot leave it.
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Basically, this ability means that if she wills to (when she is awake, that is), she can appear whenever, wherever she would on Earth (so we are goddamn lucky she's asleep most of the time), but the effective range of her movement and actions is limited to the extension of her Sea of Life, which is her "true body" of sorts. It is this Sea of Life that can extend to cover the entire surface of Planet Earth, giving home planetary range.
Her "existence in all of spacetime" is due to her being sealed and residing in Imaginary Numbers Space, which is removed from linear time, meaning beings that exist there can "exit" and act at any given point in linear time and are unaffected by causality, since from the PoV of linear time they have "always existed". BB exploits this more blatantly in CCC, and Goetia has a similar schtick with Ars Paulina.
Anyway, her range is unaffected by this because her abilities only work in Real Numbers Space aka plain old reality (reason why she was sealed in Imaginary Numbers Space), and once there they are limited to Planet Earth.
Hope this helped!
