Not a lot to go on here... but (as a reminder), Mama cats can go into heat fairly quickly even after given birth. So if she wasn't neutered soon after having her kittens she could be off answering the call of the wild to have more babies (and THAT is one of the best scenarios of where she could be!).
Tell the kind folks here some more about the situation - I'm not one to give advice, just a guy with a couple of cats and the internet. I only state the obvious.
Well we suspected she was pregnant but she just passed the first month so it's not that but mabye she had nesting in mind?
she's been gone 4 days and her last litter is 4 months old I'm worried because there are alot of nasty stray dogs around here that woudn't heasitate to shred a wandering cat and some folks keep rat poison in their garbage to " take care of " scavengers.