Major editing needed
I have problems correlating bits and pieces of the story together (like the funeral, the priest, the concept of immortality, etc.). How come did she diagnose herself as a psychopath? What exactly are her motives? More chapters would be needed to understand the plot; but for now, I'm intrigued.
Read the story now
On language, your prose and vivid imagery allows me to delve into the mind of the protagonist/narrator. But now, it's like an unpolished gem whose potential was hidden. First, I notice a plethora of padding/weak words, like 'I guess', 'I mean', or 'Ah, well'. Also, adverbs. Having them is fine, but I suggest cutting some out ('some', as in 50-70% of them). Your writing will strengthen. I promise.
Grammar. Most are correct, though the title of the first chapter...it's 'No Weddings'. Also, take a moment to revise some sentences, which look like sentences but aren't. Take a look at this one:
'The woman looked up, scanned the treeline.'
Now, I'm sure it's supposed to be a full sentence, so let's edit that.
'The woman looked up and scanned the treeline.'
Take some time to scan and edit. A rule of thumb is to use incomplete sentences ONLY if nothing is happening to the subject, or you're trying to break lengthy sentences.
On character, at first I thought the narrator was an emo-wannabe from r/im14andthisisdeep. That was until I read it a second time. Now, what I understand is that she is bored from immortality, and therefore pretends to be a psycho. If that were the case, it's acceptable. Living for 300 years would bore me to death too. But if not, write less about her personality (like 'I'm a pathological liar.' or something like that), and more about her actions. The one part where she ridicules the little girl in the funeral is a great example.
Breaking the fourth wall is amusing (I love the 'unreliable narrator those English literature teachers warned you about' part), but there are still limits. At some point, it became annoying. But perhaps it's just me, as I hate going off topic. Unless it's directly connected to the previous paragraph, either move those abrupt paragraphs somewhere else, break it into a new scene, or cut it off.
As always, I'm a sucker for dark psychology. The art of it is getting the reader to analyse the character while answering the promises you've given to them. I look forward to see your writing evolve and polished into a beautiful piece!
Good luck and happy writing!