How do I convince my little sister into something?

I have been wanting a sugar glider for a while. But I didn't have enough money to buy one. So my little sister ended up saying she could help me pay for it if it could be her pet too. So I agreed. I payed $150 and my little sister payed $70. Well we just bought the sugar glider today and we are already fighting over it. It already is going to stay in my room but im getting very attached to it. Theres no way I can share it with my sister. She is too annoying and bratty. So I want to keep it myself. Theres no way we can get another one. So how should i convince my little sister into letting me keep it? Plus she hasnt even played with it yet because she is too scared of it biting her because it bit my dad a few times lol. So what should I do to get her to let me keep it? Thanks