Help!! is my sister being fair with the cat's name?

ok well i have been asking my dad for months and months for a little kitten but he keeps saying no. i have done all the work to try to convince him but he keeps saying no. i know that if my older sister helped me, he would rethink it and then say yes. but whenever i ask her for help she says no. but then i found a perfect cat for us to adopt, and my sister finally agreed to help me. but the problem is, i don't like the name the shelter have the cat, but my sister really does. so when i told her that i would change the cats name if we got it, she said that she would not help me at all, and she would side with my dad and everything. i think it is unfair, just because of the name. what should i do? should i just not mention the name until after we get it and then name it something else? well that also sounds unfair.......?