How Does This Make Sense?

A friend is working on her taxes.  She's mostly a poor college student so she didn't pay a lot in taxes and she didn't earn a lot in income.  It would make sense to me that she would get the entire amount she paid in taxes back this year.  How is it, then, that due to all sorts of credits she actually gets tax refund in an amount that is more than twice what she actually paid in taxes?  And through the power of google, we discover she is not the only one?  How does this make sense when the government is a bajillion dollars in the hole?