Well reading the front page it seems to mee that all they do is to deblob coreboot and combine it with GRUB and another package.
Libreboot also disables Intel ME and other such unwanted gubbins, which Coreboot doesn't do (or doesn't expose a means to configure it to do so).
For a bit more context: Her full-time job is Minifree, a company she founded that sells computers with Libreboot pre-installed. Minifree has then contracted other developers to work on support for more hardware.