Why are airplanes called ‘she’?
Much of aviation has a history in Nautical terms, lore... and law.

Ships were referred to as "she" perhaps for one of the following reasons


The latin word for Ship is "Navis" which is a feminine noun
Or perhaps mostly male ship owners would name their ships after/for their (invariably female) loved ones.
Ships were often dedicated to godesses, or women of significance in order to bestow on them good luck when seafaring


Some further reading and Why are ships always female? - english.se