You could possibly copy the partition using something like mini tools partition wizard , Copy C drive to D drive and then use a disk imaging program to image the D drive to a ISO file. I have no idea if that ISO file would work with NTlite though never tried it. the Iso you create through this process wouldn't be an install-able image it would just be a clone of the deployed operating system you had and probably wouldn't work on any other computer.
in terms of why Ntlite can't do this by itself well it's pretty hard to work on a constantly changing operating system where the majority of the critical files are locked and protected from access while the system is running. even the partitioning tools need to reboot and run there own mini os to work on a live system like that.
Cloning your operating system is a useful way of getting around the windows 7 chicken and egg problem with Nvme drivers, install it on a sata drive, install nvme driver, clone the os to the nvme drive and fix the boot loader.
