> aliens may be here with us right now, she says, and we just can't see them for some reason
Actually we don't really know what we're talking about: When they hear about "Extraterrestrial Life", most people think "bug-eyed humanoids in flying saucers with a probing fetish", but chances are that 999999.9 times in a million "alien life" out there is just some primitive form like bacteria. Just ponder how many different species our planet has, how few among them are deemed "intelligent", and how far from their home planet the most intelligent ones have managed to venture so far (and for the foreseeable future).
My point is that, for all our alien neighbors know, there is no life in the solar system. Yes, it's pretty much unavoidable that "life" exists elsewhere, but there is no way we'll ever know about it, or it about us. Sad, but the harsh reality can't (or at least shouldn't) be ignored.
As for invisible aliens living among us, why should they have come? To bask in our reflected glory? If they managed to get here they are so much technically advanced we're just ants to them, so why hide? To spare the deluded feelings of superiority of some primitive life form? I'll be kind and just say "unlikely".