I think I remember when Susan Boyle first became famous that she said in an interview that she always had a crush on Donny Osmond. Didn't she say she had a poster of him in her house? So maybe singing a duet with her "crush" contributed to her being nervous. I haven't attended a concert or bought a CD, but of all the TV appearances I've seen, none were so good as her AGT debut. I think she is overwhelmed by her own success and being a "celebrity," having come from a fairly reclusive life.