I bluntly told her, "Yes, but not until your 10th birthday."
"Why?" She curiously asked, and even started counting on her fingers, "...7...8...9...10," then gave me that puzzled look.
"Most likely by that time, you're going to understand how to take care of your pet. And by that time, you'll be more responsible in feeding it and cleaning it all by yourself. You see, it's like having your own baby. You have seen me take care of Ading Mica, right?"
"You have seen me feed her whenever she's hungry and bathe her every day, don't you?"
"And clean up her mess, whenever she spills her food on the table and soil her clothes?"
"Those are just some of the stuff you need to learn to do on your own to become a responsible pet-owner."
"Ummm... okay. "
Since then, I never heard her insist on having a pet again. Instead, she would always remind me that she will finally get her pet on her 10th birthday.
Sometimes, she tries to negotiate ("How about when I turn 9, Ma?"), but I stood firmly with my previous statement. There was an article I read online regarding when is the right time to get your child a pet from babycenter, and I'm glad I did.