I used to headcanon that Gia wouldn’t have much issue getting along with Elijah’s sisters.
I still think she’d get along fine with Freya. It’s not like Freya has a lot of connections or prejudices- she doesn’t know Hayley, and she’s never known Elijah’s other lovers-. Gia was there when she was accepted into Josephine’s coven and became part of the Nola witches. Gia really helped with everything that orchestrated all that, to be honest. So I can see them getting along just fine.
But canon has- for reasons I still don’t understand, but there you have it- made it clear that Rebekah would rather Elijah continue chasing after Hayley. And so now I think that Rebekah would end up being someone who managed to make Gia feel insecure, where I don’t necessarily think she would be insecure.
Had she lived past that last scene, I think Elijah telling her “you don’t have to” in terms of how he feels about her, what she means to him, and what they are, would have made her confident. She knows Elijah. She knows those words mean a lot more from him then they would from someone else. I think she would have been fairly secure in her relationship with him, would have been more than fine helping him find a way to cure Hayley’s curse, would have supported him being around Hope, etc.
But Rebekah would probably end up making comments about Hayley, alluding to Elijah’s grand feelings for her, and it would eventually get under Gia’s skin.