If you have read the comments and advise given to the original poster in this thread, you will see that seeing as your girlfriend has overstayed the VWP she is no longer eligible to use this as a means to enter the States. Once she leaves, if she wants to return, she will have to apply for tourist visa (B) from the Embassy in Portugal.
Youre right- Immigration wont care that she was 'going' to return back after 2 weeks. The fact is that she didnt, overstayed and therefore violated the terms of the VWP.
The best bet (IMHO) would be for her to return to portugal and for you to apply for a K1 visa so that she can return to the States (in approx 8 months time) as her current overstay isnt enough for her to trigger a ban. The reason why I say this route is because adjustment of status based on marriage (without the appropriate visa) to overstay is quite a dangerous avenus to take. In the past, an overstay would be 'generally' forgiven to the spouse of a US citizen, however, it turns out that this is no longer the case. Here is a discussion about how applying for AOS beyond the 90 days of the VWP resulted in the denial of adjustment to a UK citizen.....the result....the UK citizen was detained, deported and banned from the States.
http://britishexpats.com/forum/showthread.php?t=557059
Bear in mind also, that if you do the AOS based on marriage now, then your then spouse will NOT be able to leave the States until she has her greencard in hand. Or should I say, she will be able to leave, she just wont be able to return. Yes, when you go through AOS you are given the opportunity to apply for Advanced Parole so that you can travel prior to receiving your greencard, though overstays are discouraged from using this as the overstay will still be in the system and result in a denial upon re-entry.