Dont know what to make of it

About two years ago I took my beautiful black cat to get fixed, after i came to pick her up I was told she was pregnant with 4 kittens at the time. Since then she has this habbit of picking up socks and carrieing them around like shes got her kitten. She walk around thehouse holding it for a few minutes meowing eventually coming to me to drop it at my feet. Is this a natral behavior of cats who had abortions? She acts completely normal, chases my mice through the glass and tortures our other cat. Then seeing a sock shell snap out of it and pick it up. Anyone have any ideas on a way for me to make her feel better? I think its possible shes depressed so i want to do something to lift her mood.
I did try getting a kitten into the house, that didnt work. thank you for reading, pls help!
~Tiffy~

Not all cats do it but it is normal behavior

She's not depressed, it's just instinct to follow thru with some mom type behaviour because her hormone level changed twice - first with pregnancy, then after being fixed. If it doesn't bother you, it's not bothering her.

Trouble was spayed at 6 month's old and not pregnant, and till this day carried around a small stuffed pink poodle as her baby. Some cats just do it.

Two of my boys, and one of my girls were spayed at 8 weeks and they 'mother' things too.