This is a particular case of pseudo-GTS and relative giantess. Whereas the prefix para means "next to", "related", "auxiliary"; then para-giantess means "related to the giantesses but without being a giantess".
It occurs when a woman (obligatorily of normal size) interacts with beings extraordinarily smaller than her:
Pokémon - EP0022: Sabrina shrinks the protagonists. She has never grown in size (so she is not a giantess), only interacted with shrunken beings (Ash, Misty, Brock and Sabrina's father). That's why she's a para-giantess.
Phineas and Ferb - SE2-EP13a: Phineas and Ferb create a machine that reduces them and their friends in size. Candace interacts with them and then she is shrunk, then interacts with another. Here is para-GTS theme.
Cardcaptor Sakura - EP24: Sakura is shrunken because of the power of the "The Little" card. For a few seconds, she interacted with Tomoyo (the latter was briefly para-giantess).
Flint the Time Detective - EP30: While Jean Henri Fabre is studying insects (transformed into a insect), the protagonists also become insects against their will.
Dragon Ball - EP44: There is a brief para-GTS scene.
Hand Maid May: A geek is given a doll with artificial intelligence that is programmed to serve him. There are some scenes where this doll interacts with normalwomen (para-giantesses).
Hyperdimension Neptunia The Animation: There is a SW who is sitting on a flying book all the time. Because in this anime there are no males (typical of fanservices), the rest of women in the series take the role of para-giantesses.
Those Who Hunt Elves - SE1-EP07: The protagonists arrive at a "haunted" mansion, but in reality it was controlled by tiny plant-humanoid females (the protagonists, dressed as waitresses, are para-giantesses).