Visa Extention in Portugal?

Can anyone advise me about how to go about getting a long stay Visa In Portugal?
My daughter is in Caldas Da Rainha since November and wants to stay longer than the 90 day tourist visa allows.

Where does she start, what does she need to prove and how much will it cost?
Please advise...

It's probably a little too late.... but let me know if you still need advice - would be happy to share my experiences in this matter...