Found a gift "at my doorstep"?

Say you are putting on your shoes, and you see something inside your shoe. On closer examination it is a 3 inch tall teenage girl. Well, if you would step on her, it would be to only find out she is immortal, but feels twice the pain. What a great pet toy she would make! What a great pet she would make! Would you keep me as a pet, sell me, or gift me to a pet or person? Why? Where would I be kept? When you got bored of me, how would I be disposed of?