My Art Ruined My Sister's Perfect Photo Opportunity

I love taking photos and painting them. It started as a hobby but now it’s something I'm really passionate about. I spend hours every day working on my art, perfecting each stroke until it looks just right. Last weekend, my sister came over to borrow some art supplies. She mentioned she wanted to take pictures of her cat for an entry into the local pet photo contest at a fair. I was in the middle of working on a painting when she arrived and said something about how amazing it looked. I blushed and told her she should see my photos instead, since they’re what inspired this painting. She smiled and walked out to take pictures with her cat, leaving me to work in peace. After several hours of setting up lights and adjusting angles for the perfect shot, she came back inside excitedly showing off a picture she thought was amazing. But I couldn’t help but think that my setup would have made it look better. So when no one else was around later, I set everything up again exactly as before, only this time using her cat. I waited until nightfall and took the same photos with the exact same equipment in hopes of making a more stunning picture for her contest entry. The next day, she found out about my actions but didn’t say anything right away. She looked at me suspiciously when we were alone at home last night. Now I feel terrible about what I did. Was it wrong to try and make something perfect even if it wasn't originally mine? Should I come clean now or hope this doesn't ruin her chances in the contest?