How do I convince my parents in getting me a new kitten? PLZ ANSWER NEED HELP!!!!!?

A year ago my dog died. It was very sad and me and my family were heartbroken for the longest time. So any way my dog died in june 2010 and then in decemeber 2010 we got a new puppy. The only thing though was that this puppy was a very bad puppy. Every time someone would come into the house he would pee and pee , sometimes on the people coming in the house. I know what you will be saying oh he was just a puppie , but even after haveing him for 5 months he still would do that. So one day I went over to my frineds house and spent the night. My mom called me the next morning and told me that she had gotton ride of the dog. She didn't like it and my dad didn't want it. And it also eiratated me when he would pee so I wouldn't really spend much time with it. So my mom got ride of it. Right now I am fine with that. But I want another animal. I want a kitten and I found this really cute kitten on cragislist just today. I want to get it so bad. But the last time I asked to get a kitten on craislist my mom started yelling at me and said NO. " you maybe able to get one after summer but NOT NOW!" most of the time me and my mom are best friends and she is normaly nice to me. But when ever I ask to get a kitten she gets mad. She says that the reason why I can't have one is becasue I didn't take care of my dog when we had it. But the thing is that I have a cat and I have had her for 3 years. ( the longest I have ever had a cat) So I think that I can handle another cat. And plus its the summer and this kitten will make me from going borad. So how do you think I should convince my mom into letting me buy a kitten. Plus i will pay for it my self!