Alas, poor Malaga, we...actually didn't know her well at all. Malaga's murder is the pesky thread that starts unraveling Grace's posh NYC life, but she's only on Grace's radar for about a week in the timeline of the book.
To be honest, Malaga's characterization borders on stereotypical: She's a curvaceous Colombian woman who's not nearly as wealthy as the other Rearden parents and speaks broken English. Of course, what she lacks in language skills, she compensates for with the language of lust—her womanly beauty unintentionally captivates every man she comes across. Just call her Sofia Vergara.
For Grace, Malaga represents everything she and her friends are not. At the planning committee meeting, Malaga openly breastfeeds her hungry baby (the audacity!), shocking the Ladies Who Lunch. Later, at the ritzy fundraiser, Grace notes that Malaga is the only woman in the room who's not "aerobicized and massaged, colored and coiffed, mani-pedied and Brazilled, and clothed in the most editorialized clothing (5.83)," yet the men surround her like she's the last slice of pizza in the box.
The next time we hear about Malaga, she's dead. The author doesn't give us all the nitty-gritty details of Malaga's murder, but throughout the book, we learn that she was bludgeoned to death while baby Elena (thankfully unharmed) was in the family's apartment, and her fourth-grade son Miguel finds her when he gets home from school. Yikes.
In Jonathan's letter to Grace at the end of the book, he says Malaga told him she was pregnant again in an effort to destroy their family, and he "just couldn't let her do that. There was not a single moment that you and Henry were not my first priority." Hmmm, not even one single moment? Like, not even when you got her pregnant for the second time? We're not buying it, Murder Doc.
Interestingly, the proper noun Málaga is used in a popular Spanish idiom: "Ir de Málaga a Malagón." Literally translated, it means "to go from Málaga to Malagón"―two cities in Spain—but the figurative meaning is "to go from bad to worse." We don't know if Jean Hanff Korelitz did that on purpose, but it sure is convenient that Malaga's death escalates a bad situation to a worse one when Grace finds out that Jonathan is the one who killed her.