Hi @Maryam151
3rd party bookings (you book for your sister, but are not actually staying with her) is not allowed on Airbnb. Your sister would have to create her own account on Airbnb.
Booking for friends and family
https://www.airbnb.com/help/article/427
“We’d love to welcome your loved ones into Airbnb. But to help maintain transparency and trust throughout our community, you can’t book on their behalf unless you're staying together.”