Waiting is the best answer. If you yell or complain about it there would be a big chance that she may keep it for longer, and stealing it back is dishonest, and be very very bad. I know it really stinks not being able to play such a fun game, but it is best to let time pass, and if you do really good with something in school or something, maybe ask if you would be allowed some limited time on it!
Hopes from a fellow fortniter,
-Thunderstormlover92