She had came to kill you, unfortunately for her Donnie got a hold of her.
Donnie started to hold her off as she struggled but as he did it seemed that his penis was touching her vagina and ass(the long struggle had ripped some of their clothing off) this triggered something they didn't noticed quickly.
As Marcela broke free she got her gun and was about to shoot Donnie, then both saw darkness.
As Marcela stared to see again she noticed her gun was gun as she was confused she heard her own voice saying "looking for this?" she saw herself (who was actually Donnie in her body) and got shot and died.
Donnie not caring for what happened sat there and thought what he cold do in the "new" body.
He could start to masturbate and touch his clit as he looked a his sexy new body .
He could look for sex with a hot lesbian.
switch bodies with a better looking person.
or get his revenge on the person who hired the hit person.
He would have a long thought about this.