Hi,
but then it seems you are having issues is with the location of the ns3, not fuzzylite. Pretty much the ns3 should have similar parameters to fuzzylite to be configured, like the include location and libraries. Check the parameters for fuzzylite in https://github.com/fuzzylite/fuzzylite#compile-link-and-execute , and find out what their values are in ns3.
Cheers