Tell her that bringing nature into your home is a good way to remind you to love, honor, and protect the nature that lives outside your home. Tell her that encouraging the care and trade of animals we can love and be fascinated by encourages each new generation to take joy in the natural world. The fact is that most of the best ecologists are hunters, campers, and pet owners. By demonizing these passtimes, you risk driving away the natural world's most powerful allies.
It's not about selfishness or self-interest. Simply, the people who care most about nature are those who have arranged their lives to come into contact with it most frequently.
And frankly, if I have to sacrifice the well-being of a few animals, forcing them to live in "unnatural" captivity for the edification and enlightenment of the species that holds their fate in its hands - that is, us - then I'm willing to do it.