How do sisters decide on rooms?

I'm 20 and my sister is 17. We're 3 years apart. we're moving soon and we can't reach an agreement on the rooms. One room was expanded so it's a bit bigger, and we both want that one. Since I'm the older sister, I think it's only right that I get the big room... What do you guys think? Please give me some advice!!!!!! Oh, my mom suggested swapping rooms every 2 months, which is fine but sounds like a huge hassle. + By 2026, I'll be 21 and she'll be 18 / we're '06 and '09 liners...