Why is my kitten's belly big and paws pale? Could it be worms?

Your friends are correct. She most likely has worms. You don't usually see the worms in the stools. The worm eggs are what is passed in the stools and those are microscopic so you wouldn't see them.

The worms suck blood so if she is pale I believe that is also due to worms. It makes the cat anemic; low red blood cell count. It has nothing to do with iron. You can give iron all you want but if there are no red blood cells available to carry it, it is useless.

Roundworms and hookworms are the most common worms that cause anemia. I don't know what dewormer you used but I strongly suggest you speak to your local vet about what would be the most effective. Many times what you can purchase over the counter is not the best or most effective product. Also, there are many types of worms and there is not one dewormer that will kill every type of worm. Your vet can run a fecal test to check for the microscopic eggs and then treat accordingly with the appropriate product. One deworming is rarely enough. You may have to repeat dewormings every 3-4 weeks. Your vet can give you a schedule.

Hope this helps. Best wishes.