Is it normal to have secrets with your siblings?

I (17m) just got a $30 Starbucks gift card for my birthday from my parents. I get drinks a lot but my little sister (14f) is obsessed. I asked her hypothetically at first if she would spend my card up and not tell mom and dad. She said yes obviously and so she pinky swore to me she would not say anything. Now it’s hers and our parents don’t know. Is it bad to keep it between us and never mention it?