Is it normal to be afraid of this ?

My sister has a crush on a boy she's scared to tell him. She said she's gonna tell him soon but she won't see him again till Friday. They're doing a play together. He's her age she's 23 he's 22 and he's single too. She said he's really cute and he's a great actor too. She's only done two plays with him but she thinks he's amazing. She's a little scared to tell him especially when other people around. She was shy to talk to him at first but she's getting better now. She's talking to him more. She's never told a boy she liked him before. She doesn't know what to say or do. She said he's really nice. She feels nervous to tell him. She said when she's around him her stomach hurts her heart beats fast her knees get week. She said she's never felt this way. She wants him to take her to a movie sometime there's lots of good ones she wants to see with him but she's really afraid to tell him. She wants to know is it normal to feel afraid about this ? How can she tell him ?