After Marco dies, Kim's personality starts a slow but decisive change to Marco-like characteristics. We must ask why.
Marco's ring makes its appearance numerous times, particularly throughout their relationship. Combine this with subtle hints that Marco's spirit enters Kim to be with Jimmy, the scam-loving characteristics both Kim and Marco share share, how they both had "the best time of their lives" with the same man...
Isn't it obvious?
The woman "Kim" is actually possessed by Marco post-death from season 2 on. The whole relationship is an elaborate allusion to Adoptionist Christology/gnosticism, with Jimmy-Saul-Gene standing in as the average faithful Christian, selflessly in love with Kim (his Christ and Marco) and a beneficiary of the Marco Spirit's love and miracles bestowed by Kim, all while he is clueless about the fact that Kim IS Marco. This is why their relationship works seamlessly until the absolute shock of the Howard-Lalo tragedy, and why they are able to pull off several near miraculous scams together.
Lalo, who has Luciferian characteristics, and his great evil strikes the spirit of Marco out of Kim the same way the crucifixion drove the Christ out of the man Jesus, leaving him on the cross and screaming out wondering why God has forsaken him.
We are thus left with the abandoned, dying shell of a regular woman, crucified by her own guilt with none of the Marco spirit's miraculous powers remaining, exactly as her Florida life is depicted. Like the shell of the man Jesus left by the Christ, she sacrifices herself, while the spirit of pure scammery in Marco cannot be harmed by mortal authorities.
Marco's spirit is gone after S6e7, having deserted Jimmy in Saul-Gene times.
This is also evidenced by "Gene" once again wearing the ring, but his magic schemes seem hollow and weak and flawed compared to his earlier partnerships with Marco and the Marco Spirit (through Kim), and ultimately doomed to failure.