Do you age in hypersleep? For the most part, I don't believe you do. Rebecca's citizenship award need not necessarily be current. How old was the actress when ALIENS was filmed? Because I think that would be a more solid basis for determination.
It's not uncommon for sequels to get these details wrong, however. I think the 'timeline' of Ripley's maternity leave (initially DENIED to her by the Company) on the DVD menu's makes it unlikely that her daughter was already 11 years old. And Terminator 3 ~ Terinator: The Sarah Connor Chronicles couldn't even agree with each other on when T2 took place or how old JC was at the time, leaving the 'alternate timeline' theory an unlikely explanation for the relationship between those two opposing sequels.
(It's also hard to imagine Newt surviving by herself for upwards of a year, considering that she had only 'borderline' malnutrition by that time)