Was curious about your question, so did a little research and found this:
yes, a female who's never been pregnant can produce milk. I imagine just the act of these kittens nursing can cause the female cat to produce certain hormones that would in time, cause her to start lactating.
But, don't count on this to be the only food for the kittens, it will take time for the cat to start producing milk and the kittens need to eat in the mean time.
If these kittens are not old enough to be eating on their own, then you should be feeding them with a bottle and using a product called KMR (kitten milk replacer). Which you can find at pet stores. Do not feed cows milk or anything other than KMR, because anything else is not nutritionally complete.