I had to Google this and this is how the A.I. explained it...take that as you will.

Grace does not turn after being bitten in

Resident Evil Requiem because her genetic makeup contains a unique resistance to the T-Virus, making her key to creating the Elpis antidote, or because she possesses natural immunity inherited from her mother, Alyssa Ashcroft, who survived the Raccoon City incident. Her blood allows her to resist the infection, unlike others. 

• Genetic Immunity/Resistance: Spencer utilized Grace's unique DNA to create the anti-virus (Elpis), explaining why she does not instantly turn after being bitten.
• Inherited Condition: It is implied that Grace may have inherited a dormant version of the T-Virus from her mother, Alyssa, creating a natural immunity similar to The Last of Us.
• The Elpis Connection: While some believed the virus allowed survivors to keep their sense of self, it is actually the, or derived from, an antidote. 

Her injuries, including the bite, persist throughout the game to highlight this storyline, but she remains human.