So after putting Sirin in my party again after not using her for a while I looked up and saw that I only had two songs usable and all the other songs were shaded over on the talent screen like unpicked talents(not grayed out like it would be if you didn't meet the requirements). I reloaded an earlier save where she still had all of her songs available and I did some testing. EVERY TIME I removed her from my party and then added her again the two songs that she had active would be shaded over like my previous save but i could still select them and switch between them. However, if I left the area or reloaded a save while she was out of my party those songs would be GONE. The only song that was exempt was Sword of Strength, Sword of Justice, every other song would be lost. I reloaded as far back saves as I could while I had Sirin recruited and this would ALWAYS happen to her. Here is a video demonstrating.