Something wrong with my fur baby

I found this after my fur baby used the litter box. What is it? Is it worms? She’s a year old, indoor cat since she was a baby, she’s the only fur baby that is not fixed or vaccinated. My other two cats are neutered/spayed and have their vaccines. I couldn’t afford the third one to get fixed and her vaccines. I’m saving money for it but it’s hard since I’m a first time single mom living alone. Is there anything I can do? How can I help her? Can I buy something at Petco? Or petsmart?