The movie is based on wrong premises (or "lawyer reacts to a movie", if you will)
I hope you learn something.
1. Just like many other movies, this movie wants you to believe that it's possible to completely disinherit people who would otherwise inherit, and give it to a random third person. This isn't possible. There's something called https://en.wikipedia.org/wiki/Elective_share, which means they have a right to a certain part even if the will doesn't give it to them. The fact that you you aren't on good terms is irrelevant.
2. After the will is read, Marta starts receiving stuff like the next day as if the inheritance process is already over. We've seen other members were more than willing to contest the will so this would be a long process lasting weeks, months and even years before all appeals are resolved and the process finished. Also, there's a criminal investigation going on, for fuck's sake. The movie creates this feeling of urgency for Marta, which doesn't make sense.
3. Marta and her mother start receiving stuff and they are like "What do we do with all this stuff?" Why are they moving stuff from Harlan's house to her residence? This was the stupidest part. Are you emptying Harlan's house? Why? Are you also going to rip the house out of the ground and place it in front of Marta's residence lol. Simply leave everything in Harlan's house as is and when the ownership of the house is transferred to Marta in the land registry, she'll be able to live in Harlan's house and do what she wants with all the stuff. Is she supposed to move all that stuff back into Harlan's house? This scene in the movie was really retarded.
4. Slayer rule. Ah yes. In the movie it's black and white. Either she applied the correct bottle and she inherits or she applied the wrong bottle and she doesn't inherit. In real life, the slayer rule applies only if it was murder. Murder means that there was an intention to kill beforehand. Something like "I'm going to kill this person and I mean it". What Marta did (if we assume she took the wrong bottle) was involuntary manslaughter. That's a different thing from murder because there was no intention. The slayer rule applies only if there was murder. It doesn't apply if it was involuntary manslaughter. So Marta would inherit either way and which bottle she applied doesn't matter at all. Furthermore, if somebody were to argue in court that Marta had an intention to kill Harlan, that would break apart even more when we realize that she wasn't aware that she's in the will, so from her perspective she wouldn't gain anything and so we can't invoke the slayer rule when Marta couldn't even expect to inherit. The slayer rule is when you expect you'll inherit because you murdered.