My sister and I will be working together for the rest of our lives

I've been home due to COVID so I've been spending time with my sister. She's noticed how grown up and attractive I am now and so have I. We've been bonding a lot and falling for each other and will soon be engaged and married. I imagine most of you have had budding relationships like that so I thought I'd ask you how to propose so I can make it as special as possible. Her favorite sport is tennis.