"G girl" is LGBTQ slang for a genetic girl, meaning a cisgender woman.
In other words, a "G girl" is a woman who was assigned female at birth and identifies as female. The "G" likely refers to "genetic," highlighting that her biological sex aligns with her gender identity. This term can be used to distinguish cisgender women from transgender women, although it's important to note that using such terms can be sensitive and should be done with respect and awareness of individual preferences. The term isn't common in everyday conversation and is primarily used within specific LGBTQ+ communities.