»Why was Sati allowed to return?«

I think I've got most of the film but I'm still a little confused with the part of Sati.
Why was she allowed to return to the Matrix from the Train Station?
What was the deal that her parents had worked?

Only thing that I came up with was that the machines were aware that Smith was out of control by this point and that he had made his changes to the matrix (ie rain, etc) so Sati was an attempt at balance - return the sunshine.

Cheers
B

sati was a program created by her parents out of love. since sati was created without purpose, she had to be smuggled into the matrix via Merv and train man. the deal her parents made with Merv was that they would give the Oracle's termination code in exchange for Sati's safe passage. we know from Enter the Matrix that the Oracle trusts Rama Kandra and his wife and that Sati was going to be very important for the future of humans and machines. that's why she made the choice (mentioned in M3 when the Oracle was explaining her change of image to Trinity and Morpheus) of giving up her termination code. but she probably had a backup code along with a new disguise, which is why her image changed. the importance of Sati we find out at the end of M3 is that she becomes a highly evolved program with complete free will and without purpose...something that programs (who were not exiles) didn't have before the Matrix was reloaded the 6th time. a lot of people speculated that her control of sunshine was her new purpose. i personally don't think it's her purpose at all. she chose to do it because she had the power and free will to, and she did it for neo out of love. love was one of the main concepts the machines assimilated into their system before the 6th reboot due to neo's love for trinity.