Oh sorry, I misread your post (it was late). You can't merge annotations - it's just not supported, as there are too many things that can go wrong because there is no way to uniquely identify annotations to understand when annotations have been edited or removed. You can use multiple layers and have her annotations in one layer and your annotations in another layer, but that will only work if you only annotate on one device at a time before synchronizing changes. I may support an option in the future to choose which layers are synchronized (based on layer name, as it would be far too tedious to try to provide a selection UI where you could dig down into every page of every song to pick individual layers).
Mike
Mike