Both are correct.
In 1) "Ihres" substitues "ihr Buch". So 1) becomes "Ist es es ihr Buch, Frau Schmidt? Ja, es ist mein Buch." in the long version.
In 2), if you substite "ihr Album" accordingly, you get "Ja, das ist ihres."
I just looked it up and apprently "ihres" appears as Possivartikel, whereas "ihr" (ihr Buch, ihr Album, etc." is actually a Possesivpronomen.