How do i retrieve backpay?

Hello! My daughter was finally approved for SSi. They sent her acceptance letter and first check last week. It says her Backpay should be there by Sept 29th. I wondered if that check was supposed to come with her monthly one. Do they usually send it via check? Or do i have to call to have it deposited? I am only asking because its 2800 dollars and i am worried about a big amount like that being sent out by check. I dont trust the mailmen today so... just wondering what should i expect?