If its tender but soft, you may be okay. Could be anything from a number of inflamed organs (bladder, kidneys, etc) to infected mammary glands if she's still nursing.
If its a hard belly that could mean serious internal bleeding and/or intestinal leakage.

You really do need to get her to a vet, even if its not your regular one.

 

@samanthavee, thank you. Our regular vet is the only vet in town. The next vet is over 100km's away. I unfortunately cannot palpate her belly, she will scratch you if you so much as a accidentally touch her tail. She may rub against you, but beware she thinks you're touching or moving to touch her. She is still acting normal, eating, taking the kittens hunting, letting them nurse, etc. Which now has me wondering, what are the chances that she's pregnant? It's a bit early, the current litter was born first weekend in September, but if I understand the internet correctly it is possible? I bred dogs, never cats so I'm a little lost. Previous litters were born and raised in the barn, now for some reason she's decided to stash them in my washroom since the were roughly two months old. Until then they lived in a hollow under a huge old fallen tree.