The ending to A Thousand Splendid Suns is a beautiful ode to Laila and Mariam's relationship, which is the foundation that the novel is built on. It emphasizes how Mariam and Laila became family and how Mariam's love still lives on after her death.
Here are the things that you should remember when you read the ending:
Mariam and Laila became like mother and daughter.
Laila wouldn't have been able to renovate the orphanage without Mariam.
The two women found each other at just the right time. Laila, having recently lost her parents, was desperately in need of a mother. Mariam, on the other hand, was traumatized by her numerous miscarriages and Rasheed's abuse. Laila needed to be loved, and Mariam needed someone to love. They both find what they're looking for.
Eventually, Mariam ends up doing the thing that only a mother would do: sacrificing her life for Laila and Laila's family. Laila is so grateful that she leaves her comfortable life in Pakistan and dedicates herself to the children of Kabul. Mariam has a hand in this, too, because Laila uses her inheritance to fund the orphanage.
This leads us to the revelation that Laila, now a teacher, is pregnant with a child. The family loves to brainstorm potential baby names (like Zalmai, we have no idea why an "Afghan boy can't be named Clark"), but they never discuss girl names (4.51.44).
That's because Laila already knows that she'll name the baby Mariam if it's a girl. It's a small gesture, sure, but it's a powerful one. We've already seen how Mariam is in "Laila's own heart, where she shines with the bursting radiance of a thousand suns" (4.51.37). Now, Mariam and her story will live on as a part of Laila's family, where she always belonged.