arrears of uc

wondering if anyone has an idea of what will happen in practice here.

client with a learning disability. starts work in full service area. due to earnings she has no entitlement to payment of uc but i get her to put in lines to be assessed as LCFW for both a LCFW element and an earnings allowance.

claim was made in dec/jan so before changes to wrag payment.

this month claimant gets put into wrag with LCFW backdated to march.  the additional component and earnings allowance now mean UC due.

when/how will she get the backdate?