New sibling adjustment

Just had my lb 2 weeks ago and my 2 year old has been great with him up until today. She’s been obsessed with kissing him, talking to him, helping out etc and always loved the babies at nursery/ her dolls. But out of nowhere today, as she was kissing him, he cried out- nothing unusual and she freaked out and every time he’s made a noise since she’s been hysterical!! It’s like she’s petrified of him now and won’t go near him. I fully expected her to struggle with having a sibling as she is such a mummy’s girl and is really attached to me. I’m just not sure what’s happened?! Is it an attention thing? Is she just overtired and going through a lot of emotions? She has just moved up into the bigger room at nursery which she is enjoying but I do think she has found overwhelming. Anyways just wondering if anyone else has experienced their toddler crying whenever the new baby cries and how long did it last?!