Is it an absurd notion? Perhaps. On the one hand, Gipsy Danger and Godzilla are both main protagonists who fight Kaiju for a living and have never been seen in the same place at the same time, but on the other hand, the same can be said of Superman, and he clearly can't be Godzilla (sure, Batman could pull it off, but that's neither here nor there).
In any case, there's no way Gipsy Danger could be Godzilla, because she doesn't have a tail.
Oh.
Well, Godzilla only has one tail, and we got to see Gipsy Danger use both swords at the same time when-
Oh, right. We didn't.
Moving on, Godzilla had the power to fly via jet propulsion in one movie, and Gipsy Danger can't do that.
Ok, then.
Well, Godzilla is organic, and as we all know, anything that looks like a machine and has people piloting it is definitely a-
Huh. You know, that would explain why Gipsy Danger is immune to EMP a whole lot better than the explanation given in the movie.
Godzilla's power varies wildly depending on the story, and since Gipsy Danger has only appeared in one story, the same cannot be said for her.
Oh, yeah. Gipsy was a lot weaker in the novelization, wasn't she?
Speaking of "she", it's never been clear exactly what Godzilla's gender is, while there's never been any confusion about Gipsy being female.
Or perhaps I spoke too soon.
Godzilla is known for making loud vocalizations.
Hmmm, that's true. Gipsy does blow a very loud horn to announce her presence in Anchorage.
Godzilla has a habit of stealing the glory.
Yeah, I guess that whole sequence qualifies.
Time to get serious.
In most incarnations, Godzilla is awakened and empowered by nuclear radiation.
Great. Now the images are getting recycled.
Godzilla can function underwater.
%@&#! Not again!
Godzilla can survive a nuclear explosion.
Godzilla has died and returned.
Godzilla has made use of energy-based attacks.
Uh...
Ah ha! Gipsy Danger can't shoot nuclear fire as an ultimate weapon!
...
Well, at least now we know why Godzilla often looks like a man in a suit.