What a cutie! Certainly not the expert here, I decided to play around with the “antiquing” angle.
What I did (in Paint Shop Pro 8):
1. Duplicated layer
2. Applied a Gaussian Blur to the duplicate layer
3. Chose ‘Overlay’ blend mode with a 75% opacity
4. ‘Colorized’ the original layer: Chose a yellowish/sepia color and gave it minimal saturation.
5. Cropped the image to a square.
6. Added noise
7. Created a mask around the edge and used fill tool with a color found on the girl’s jacket to create a mild vignette.
8. Applied a Gaussian Blur to the mask
9. Added a white border
This was fun! Can’t wait to see what others come up with!