its not like this, Simple when you deliver the order you have attached that image. So when she mark the order completed this image was reaady tobe shown on your portfolio. (At that time while giving Review she have the option to Click " - " minus then it wll make the portfolio image hidden.i.
But Now as its already done… you have 2 Options.
1st: Tell the buyer to see the order page and see if she have the mofify feedback option still available… if yes she can remove the image by cliking " - " minus and the image wll be not shown then…
2nd: if no option to modify tell her to Contact CS and open tickry with order issue and option " Chnage the feedabck" then the issue wll be soved and she can modify the feedabck and remove the image.