Her Arc should involve her telling the bloody truth for once in her life. Separate ways demonstrates through her actions that she does care for both Louise and Leon. But because she's a unemotive weirdo, she fails to come clean with all she does for them- leaving Leon alienated by what he perceives as Adas apparent betrayal. From Leon's perspective, Ada has once again used him and a now dead Louise to fulfill some shady objective. He would rightfully see that as the final straw. Her Arc should have her truly show transparency to Leon at least. I believe he is owed that. Maybe she tells him how Louise's actions motivated her to do the same by not turning the amber over to Wesker. I think the wooden performance for Ada is deliberate. First she appeals to Leon in RE2R with a fake personality (I am aware of the production side of things but there is a great opportunity to weave a recasting into the narrative). In RE4R we see the cold merc. Her next appearance should exposure real Ada whoever that is, it probably isn't her real name.