Invisible Passage - Tricky wording on this ability, need clarification

There is an ability that a CR 3 Green Hag gets called Invisible Passage. It's an action she can take to turn herself invisible. The stat block, word for word says:

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Invisible Passage: The hag magically turns Invisible until she attacks or casts a spell, or until her Concentration ends (as if concentrating on a spell). While Invisible, she leaves no physical evidence of her passage, so she can be tracked only by magic. Any Equipment she wears or carries is Invisible with her.

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How would you rule the part about "leaving no physical evidence of her passage, so she can be tracked only by magic? Does this imply that her footsteps leave no imprint in mud or grass? She leaves no trail on dusty cobblestones? Does she still make noise that the players can hear to try to detect her location?

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Sorry if this should be obvious. Also I'm assuming that she gets advantage when attacking from her Invisible passage on a turn, such as taking an opportunity attack or an actual action to attack.

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