SSI retropay confused?

When my child was born prematurely she was able to recieve ssi benefits but in 2008 when she got older she stopped recieving it cuz they said their was nothing wrong with her, but now it turns out that she was diagnosed with A.D.H.D and A.D.D which makes her eligable, I've already spoken to a representative at the ssi office and she said Yes she will be recieving benefits once again, but couldnt tell me if it be retropaid from 2008 or from when we reapplied for the benefits which was jan of 2011, can anyone please shed some light this situation please thanks in advance:)