My cat rosie gave birth to 4 kittens, but still holds some inside?

my cat rosie has gave birth to 4 wonderful kittens yesterday, she lets me stroke her belly and i can feel she has more inside, im getting extrememly worried that she is struggling to give birth to them, i have read and been told that she can give birth upto 48 hours later, what shall i do? how can i help her? shall i take her vets?