You can Gmail it to yourself via your 3DS.
Here's a couple steps on how to.
1. Take the Screenshot on your New Leaf game
2. Press the Home button and enter the Internet Browser
3. Type in on your search bar "gmail"
4. Once loaded press the link that shows "Gmail"
5. Enter your gmail + password
6. Once in, it will say the browser has taken you to a basic html version of your inbox, don't worry about it as it doesn't matter.
7. Look onto the left and see that there's an option called "compose mail", click on it.
8. There should be some info there, where it says "To" put
your gmail. On "subject" simply put what you want to title the mail.
9. Where it says "Attachments", click the "browse" option, doing so will cause your photos to load up, click on the photo you want to send. Make sure to type something on the big text box or else it will fail to send.
10. Once done simply click send, then enter your gmail account on your phone, and you'll find your screenshot!