My fanon: After getting married, Fluttershy LOVES being Discord’s pet on a frequent basis*, and doesn’t mind when he adds variety to her form. This time he just tweaked her legs a little for the socks he poofed onto her. She enjoys this pleasant surprise and await her curry-combing, mane and tail brushing and/or love making/breeding (they have many children, because children are both adorable and in need of lots of care, and also great sources of Chaos).

*He has made DIRE threats regarding anyone who allows her to discover the more common definition of “pet play”.