Fragments were a recurring issue through this person’s story, seen here at the start (“Kayla had known Mateo since she was ten. Their friendship spanning fifteen years.”) and the end (“Elsa was off doing some research work in the middle of the ocean. Though Kayla suspected that she would be home soon for the wedding.”). I improved these for flow.

I removed “fifteen years ago” since, later in the paragraph, we learn that they’ve been friends for “nearly two decades”. Fifteen years isn’t nearly twenty, so I opted for the longer timeframe.

There is a lot of clunkiness, such as the sentence, “Mateo had gotten along well with her, a few years older than her, he had told her she reminded him of his sister.” I rewrote this and included part of the previous sentence for better readability.

I didn’t like the sentence “Kayla had been a loud, chubby kid and that was something that never went off well”, as it’s not clear what being chubby has to do with things never going “off well”. I changed this to “obnoxious”.

The last few sentences are a mess:

• It’s not immediately clear that “his sister” and “Elsa” are the same person.
• “Now, after almost two decades of friendship Elsa was her best friend. Mateo might be her oldest but Elsa was definitely her best friend” is awkward and, frankly, unnecessary. It doesn’t make a difference that Mateo was the “older” friendship, readers just need to know that he no longer is.
• I changed Kayla “suspecting” Elsa would be back to “hoping”, since it doesn’t make much sense to “suspect” she’d be back unless she knew something about Elsa’s schedule, which, at this point in the story, doesn’t appear to be the case. Given that Kayla is having a miserable time during this chapter, having her “hope” for her best friend’s return works much better.