So if i understand it right you think that Amber meeting Great Ocean was an immaterial thing through her connection with the originator of her monster line, and that it happened while she was still at the same lake Tanos sent them, well i honestly didn't have that impression.
I don't think we can say for certain that the twins were still physically at the same lake when Amber sees Great Ocean, plenty of the comments made by her at the time are about what she feels with her body and the process of "dying":
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She feels both the blinding light and the hot water
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Her eyes adjust to the light
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Her eyesight fades due to the loss of blood and oxigen
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She feels that she can't breath
Even if we take that some of those feeligs were due to her "real" location most things seem to be reactions to whatever the place Great Ocean was.
As for how they returned i don't think it would be a problem either to Great Ocean or any strenght eater to return them, the only thing we need to consider is purpose.
Also at this very moment there is a sound effect, it's not one of someone being bitten but instead seems like one of a power being used, i wonder if it's the sound of the strenght eater teleporting amber to Great Ocean
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The sound is however different from both Liz and Nico's teleportation
Lastly i'm not sure if we can say for certain that Amber was infected by a strenght eater, her different power set could indicate that Great Ocean was the ond who did it, and this could be the case if she was sent to his dimension.