Dream sequences are a great way to get inside of the mind of a character. Think about The Dude's dream sequence in The Big Lebowski, or (spoiler alert!) 80 percent of Inception. Dreams allow us to get inside the subconscious of a character, where all the icky and unpleasant stuff lives.
Laila's dream sequence in Part Three of A Thousand Splendid Suns is no exception to the rule. Her dream of burying Aziza alive reveals that she feels like she's complicit with the oppression of women carried out by the Taliban.
Like all dreams, Laila's nightmare is sparked by real world events. Mariam and Laila had spent the day prior burying their television in the backyard, "striking the ground with a spade, then shoveling the loose dirt aside" (3.40.2). The Taliban had been raiding homes looking for illegal media, and the pair decided to hide the TV until the raids die down.
The Taliban's moral laws are carried out in two main ways: banning media and oppressing women. Laila's dream connects these two missions. The television gets transformed into her daughter, a young girl who has never had the opportunity to go school or even play in the streets. This is Laila realizing that she has been forced to hide away Aziza, just like she hid away the TV set.
Laila tells Aziza that it will "only be for a while," but that doesn't keep the young girl from panicking (3.40.63). Laila worries that the Taliban's oppression of women could get even worse, and her fears are realized when Rasheed forces her to send Aziza to an orphanage. Naturally, Aziza's gender has a huge impact on his decision.
Don't forget that shovel, by the way. Here, it represents the oppression of women, and it comes back in the end of the novel as the weapon that Mariam uses to kill Rasheed. It goes from a symbol of oppression to a symbol of liberation—liberation, it must be said, with a heavy cost.