Edit: I used a pic of Kiri from Avatar as a reference for this bc her and Hallow are kinda similar

Ref pic:

Instead of being a scrap, Hallow is now written as Tre's older step-sister.

She's still French

She's not human anymore either, she's actually an unknown vampiric creature mimicking the form of a human

She also feeds on humans instead of animals (but goes absolutely feral for any type of raw meat)

Since Stone ran away from home, Hallow took the initiative to (secretly) be Avrille's new "lab rat" except instead of testing candy on her, she studies Hallow in hopes to find out what she actually is. Hallow also doesn't know about Avrille experimenting on Stone in the past

When it comes to aging, Hallow's species (including herself) are immortal. Among her kind, her undead life is only just beginning. Hallow can still be killed, but it's an incredibly complicated process. She also isn't stupidly overpowered either.

Her appearance in the above photos isn't actually what she looks like: it's an illusion used to lure in prey (and to fit in better in hopes of having a social life in Hallow's case)

Despite her bloodlust and instincts, Hallow has sworn off feeding on members of her family (including Tre even though they both bicker a lot). She also refuses to feed off of Maroon due to feeling a strong emotional connection to her.

Despite how she's viewed amongst her own kind, among humans, she is viewed as a grown woman in her early to mid 20s. Although it is unknown how old she is exactly.

Tre and Hallow's friendship as siblings is far healthier than Avrille and Stone's, but Tre often finds her annoying.