Update:
Scan dat 16/01. Called this morning and my daughter has been awarded MRC & LRM from 13th December 2023 - 27th July 2027. Backpayment was issued a few days ago, but somehow they've sent it to a Halifax account (I've never been with Halifax, I'm with Santander), so they're recalling the payment and reissuing it. Que a different kind of anxiety..