Im at the other end of the scale, measuring 2-3 weeks larger thanmy pregnancy.
There is a bit of leyway with size as the baby can be lying differently when measured but they will always err on side of caution if there is any reason why baby may be small or large. In your daughters case, because baby may not have grown since the accident they are being ultra cautious.
The protein can be a sign of pre-eclampsia but also a sign of infection in the urine or discharge. If possible tell your daughter to always take a mid-stream sample where any discharge may have been washed away as such before the sample taken.
They have given your daughter the info based on the extreme ie baby not growing at a good rate, but im sure that if they had serious concerns then they would have advised to immediately go for a scan.
The backache may mean a concern of a UTI or kidney infection, not sure why they have told her to go straight to hospital though, but follow the advice theyve given,