In a nod to the original Japanese films, Mothra was worshipped as a deity by a primitive culture living in the Yunnan Province more than 10,000 years ago, possessing a mutual symbiotic relationship with them - Mothra's human worshippers used a temple to protect her egg, and Mothra in return would protect them from predatory Titans after hatching.
She only uses that attack when she knows she is going to die, though, because the extreme loss of scales will cause her to lose her flight.
Or, perhaps it will have already gone through its chrysalis transformation and from the start Mothra will again be in her adult imago form.