Continuity mistake: When Frank pursues the killer at the lake house, through the snow-clad forest, his breath doesn't show. But he comes from a warm house directly out into a freezing night air.
Continuity mistake: In the scene where she takes him into the boutique, she goes into a dressing room with a curtain across the opening. The shot pans from looking over the curtain, where it has 5 ruffles, to Kevin Costner and then back over the curtain which now only has 3 ruffles even though she hasn't come out. (00:27:45)
Answer: While she did it high on drugs I don't think she actually regretted her actions that much. She had months to track down this Armando and cancel the hit. Also she 'paid him in full, and then some' so like surely she wound't have taken the kinda cash the first time she went to find him and ask him to do it.You don't have a sudden fit of jealousy while high with loads of money that just happens to be ready to go. Must have been two separate meetings. She was jealous and hateful deep down inside and it came out while she was high and then once it started she was didn't stop it.
She didn't want to stop it until the young boy Fletcher was almost killed in the boat that the guy the Hitman booby trapped she just didn't want the boy hurt but she always wanted her sister to be done with.