Why does my dog get possessive of socks and shoes?

it usually only happens at night and late night. 8 pm and thereafter. basically, whenever i take off my shoes in the evenings, the dog walks up to them and protects them. she will sit in front of them and protect them like a guardian. we wouldn't even notice until we would walk by and get a surprise attack. if we try to move the shoes with our feet, the feet become enemy #1. as if they are not attached to me, her ever so loving owner. i can pick them up with my hands, no problem. i think she was kicked a lot before we had her, we got her from a no-kill animal shelter. i think it may also have to do with the fact she could be more tired at night, and gets into some sort of "mode", and kind of changes her behavior at night. i could understand what others might say about the scent of shoes, but what about the change in behavior.

she is a min pin, 2-3 yrs old, and fixed (but wasn't broken).