I don't even think when we see Mab on Earth that she in her entirety is even on Earth. I go along with what others have stated that the construct we see on Earth is a whisper of power from that other being which resides within NN.
The NN is walled off from Earth with a threshold. Those being that exist within NN lose power when crossing that threshold.
I think the only being that could extend a complete invitation to cross the threshold without loss of power would be Mother Earth.
Gotta take issue with this interpretation, my brother:
A threshold is established by the beings that inhabit a space (structure/building whatever). I see no evidence--in the DV at least--that a world sentience/personification of the earth even exists, and in the RW posit that, if it does (big if), it's some form of "collective consciousness" of which all living inhabitants are a part (while ironically being unconscious of it, for the most part).
There has been some suggestion that fire ants, for example, may represent a "hive mind" that extends over many square miles, incorporate millions of nests and billions of individuals. Similarly, Acacia trees can chemically communicate their "distress" when fed upon by giraffes or elephants, such that neighboring trees in a radius of several miles increase production of tannic acid to make their own leaves less palatable. But this is a long way from extrapolating a worldwide consciousness.
Therefore if a threshold exists, it would have to be generated by the beings inhabiting the earth in this dimension. For a variety of reasons I think that would be difficult to maintain on a worldwide basis. It may depend on the nature of the beings seeking to cross from the NN--since the Fae or largely of human origin, they may not be inhibited by "threshold" effects, if these exist between NN/our world. Some of the really evil bastards might have more trouble.
Historically, at least in RW beliefs (including my own), other sentient beings besides ourselves have inhabited this world. Jinni, for example, were once earth's sole sentient inhabitants until they departed to "al-Gaib"--the Unseen Realm--which is close enough to be considered the NN in my book. And at lease some of them readily move back and forth between dimensions.