Inkling Girl is the default design of the Inkling girl of the Splatoon series. The poster girl, if you will.
She is also the character played in Super Smash Bros Ultimate.

She will generally look like this (from Splatoon 1, 2, and 3)
post #2616572 post #2749850 post #2622654

of course, she can wear different outfits, have different skin tones, and have different hair colors.
But the design in the face area (facial features and hairstyle) will usually stay the same

The moment the style of her face or hair is changed is no longer Inkling Girl but should just be tagged Inkling