Maria, your sister is a good model, and you've done a fine job! Welcome to the forum. I look forward to seeing more of your work and more shots of your sister. Have you tried a self-portrait for the weekly assignment?
The Weekly Assignment photos have to be taken during the week of the assignment. The Monthly Assignment have to be taken within the month of the assignment. The cut-off times and rules are posted at the top of the page on each forum (I think). We will be starting a new Monthly Assignment probably any minute now as Fred will take the ones from August and select the finalists for us to vote on. And announce the new theme for September. I think you will really like the assignments!