The manuscript is currently undergoing evaluation by my proofreader, 'Cuzzie', who will report back - warts and all - by the end of next week. Hopefully, she won't find too many warts, so publication should follow very soon after that.
'Larussi's Heartsong' is listed as 'The Appendix to A Queen's Heart', but it is really a self-contained story. It draws its roots from the trilogy, but it is not necessary to have read that before reading this book. All the information you will really need is included in an author's note at the beginning.
All the same, I recommend that you do read the preceding six 'Avalind' novels (this is the seventh). Only that will give you a full flavour of the world in which the books are set. The previous six books are the 'King's Head' trilogy ('Usurper', 'A Sovereign's Honour' and 'A New Queen Rises') plus the 'Queen's Heart' trilogy ('The Ancient Realm', 'The Shattered Realms' and 'The Power of Four Queens').
'Larussi's Heartsong' is something of a departure from the tone of its predecessors. Don't worry, Fantasy and Action fans, there is still plenty of excitement, but the focus has shifted slightly.
When we last saw Larussi, she was a heartbroken thirteen year-old girl, who had lost everything, and everyone she ever loved. At the conclusion of 'The Power of Four Queens', she is taken in by the Sisters of Mercy, a religious order in Dragotar, who care for her. There, she unrolls as a postulant and rediscovers her childhood talent for singing. Five years pass and Larussi grows into a young woman of astonishing beauty. The new head of the order, Mother Sulsa, knows that the postulant Larussi can never be a true sister of mercy, so she must go forth into the world once more.