Astory's main theme might be difficult to figure out because

the pronoun reference replaces a noun, but you have to make sure there's no room for confusion.

in the first sentence "her" could be referring to shely or to the sister. the answer there is "shelly called her sister and told her about the new baby."

in the second sentence "it" could be referring to the roof or the floor. the answer there is "since the roof leaks on the family room floor, we need to repair the roof."

the sun warms our planet, and with the moon, creates the tides. the moon orbits the earth and in turn, the earth orbits the sun. because they appear to be the same size in the sky, the sun, earth and moon work together to create eclipses. when the moon is directly in between the earth and sun