really depends what she’s terrified of to say if it’s normal or not. it could be totally normal – it is a totally new stage, and new things can be quite scary. (and hormones can be quite wacky when one is engaged).
or like s2021 says: it could be she is having serious doubts for very good reasons.
so she should talk to someone who has lots of experience with shidduchim and is WISE!
s2021 – just read in detail what you wrote (before i skimmed) – that is scary and so sad. 🙁