1) Baby elephants get abandoned because their herds fear that they will attract lions.
2) When Rachel found Suni, she took care of her, and it made her feel sorry for baby elephants. So now she's dedicating her life to saving those baby elephants.
3) The nursery is situated close to Ngoma National Forest because it's where most of the elephants live.
1)I think the "Leaky Bucket" that the author is referring to means the "Problem" that they're facing.