She declined to comment further, saying she hadn't meant for her post, which was shared widely on Facebook, to "blow up like this".
Restaurant Brands spokeswoman Amy McKenzie confirmed a complaint had been made by Blackburn.
"As with all customer claims [we are] taking this very seriously and investigating the matter.
"KFC has been in contact with the customer to get further information to help with those investigations and to gain a better understanding of the food journey once Cassandra left the store."
McKenzie said it was unlikely the eggs would have come from the KFC store due to the strict food safety procedures and systems in place in all KFC stores.
"The KFC restaurant at The Base, Hamilton had a pest check visit at 8:15am on the same morning the meal was purchased. The pest check report found no pest activity."
McKenzie said cooked KFC chicken was held in cabinets at temperatures of 60C or higher.
"Research has shown that food that is warmer than 40C is repellent to flies and potentially fatal to their eggs and maggots."
Last year a woman said she found fly eggs in her KFC popcorn chicken, bought from a Pukekohe store.
In 2012 an Auckland family swore off KFC for good after finding maggots in a piece of chicken bought from Botany Downs.