Track 30, the last one, from the soundtrack.
This is the song which Sara and her mother used to sing together. Singer is Sara's seiyuu (voice actor), Saori Hayami.

Japanese lyrics (just written by me so it most likely have errors):

Ro takaku noboru hikari
wakitachitaru omoi
mamorubeki ryu no michi yo
shira ha sasu sora o aogi

Suna kaze arabutomo
sakihokoru ko no hi yo
hana ni mai chiran

Rasen ni tsutau hikari
ryu no te wo tatsu niwa e
arishi hi no omokage yo
towa no uta wo kokoro tsunagi

Ten ara madoutomo
moesakaru ware no hi yo
yami wo kirisakan

Ro takaku noboru hikari
nagareruru toki kioku
ayumubeki ikiru michi wo
yueni ikiru sora o aogi

English lyrics (the part what was translated in the movie):

The light rising above the tower
thoughts boil and run high
dragon path to be protected
pierce with shining blade look at the sky

Sand, wind may rage proud blossoming
bright sun dance in flowers and never will it die

The light flowing in spirals
to the garden where the dragon's claws ends
shadows of the olden days...