The Last Sovereign was produced completely for free over the course of ten years and remains free to this day! This DLC exists for those who want to give a purely voluntary donation to support the game's development. Aside from attaching the game to your Steam library, it does not contain any additional benefits for TLS, all of which will remain free.

That said, Yarra may visit your hard drive to offer her thanks. If you check your game folder (Steam Library > right click TLS > Manage > Browse local files) you may find a little gift from her. ^-^