How does she get the numbers?

Okay I may have missed something, but how does she receive the numbers in the compound? I assume that they receive them encrypted somehow - but then, why does they need to send out the numbers in the first place? Why not use same technology to send the encrypted message directly to the receiver, without going through the numbers station first? Seems unnecessary to go through the numbers station?


*possible spoiler*

..and another thing - she clearly has no idea what the numbers mean - how is she then able to send out a message she has written herself?