Explanation for the ending of Carrie?

I think it is meant to mainly be open to interpretation, however the following excerpt from stephenking.wikia.com I feel gives the best explanation you could hope for.

[Carrie's mom]... brought Carrie to her knees so that the two could properly pray together. Meanwhile, Margaret had "snapped" earlier on and hidden a knife under one of the floor boards to stab Carrie with, having fallen to the belief that her daughter was ruled by Satan. While they both recited the Lord's Prayer, Margaret stabbed Carrie and caused her to fall downstairs, backwards. She then stalked the frightened child throughout the house, eventually backing Carrie into a corner. Finally, Carrie used her powers to "crucify" her mother to the kitchen doorway.

When it was over, Carrie was overwhelmed by guilt, grief and rage. She screamed to the top of her lungs and grabbed her mother. However, Carrie's powers "spiraled" out of control and caused the house to collapse around her and her mother. Quickly removing Margaret's body from the doorway, Carrie raced for the kitchen closet where she spent many nights being forced to pray for forgiveness and shut the door. Within, Carrie was hit in the head by falling debris and killed. The house was also set aflame due to some of the lit candles falling down, and it eventually sank underground, taking Carrie and Margaret with it.

In the book...

Carrie kills her mother by stopping her heart, but nothing happens to the house. Instead Carrie dies later from her wounds in Sue's arms.

In addition to the explanation from the wikia article, I am also reminded of the scripture in the Book of Revelations from the New Testament which describes the shame of the wicked after the sixth seal is opened -

Revelations 6:16 - ...and they said to the mountains and to the rocks, "Fall on us and hide us from the presence of Him who sits on the throne, and from the wrath of the Lamb..."

I think the house collapsing is supposed to be like her own personal Apocalypse and like the wicked in Revelations, she is calling up the mountains and the rocks to fall upon her and hide her shame for her "wicked" acts.

From the book Interviews Too Shocking To Print! Conversations with Horror Filmmakers and Their Accomplices by Justin Humphreys:

Originally, Carrie was supposed to end with Carrie White's house being demolished under a rain of stones, like in Stephen King's original novel. But the conveyor device that was supposed to pummel the half-scale model of Carrie's house with rocks malfunctioned, so Fisk had to burn it for the scene. However, insert shots of stones smashing through Carrie's roof snuck into the finished film, and in Carrie's closing scene, as Sue Snell (Amy Irving) goes to place flowers on the ruins of Carrie's home, the spot is buried in stones — an odd continuity error arising from the rain of stones' deletion.

In fact, there was a deleted scene, also from King's novel, that De Palma shot which would have established Carrie's telekinetic ability to make stones rain down. In this flashback, Carrie's neighbor (played by actress Tina Romanus) is sunbathing and young Carrie curiously asks her about her breasts, at which point Carrie's mother (Piper Laurie) beats her. The enraged Carrie subconsciously fires up a hailstorm of rocks. Photos from this deleted scene pop up occasionally.

The malfunctioning machine wasn't the only reason why the demolition scene wasn't executed as planned:

When Carrie returns home after her prom meltdown, the script had called for the house (designed by Spacek's husband) to be destroyed by a volley of rocks. In the end, however, Auer's machine for hurling the rocks lacked the power to collapse the house. The shoot was running late at 4am and the police had been called about the noise, so De Palma opted for simply burning the house down.