hi luca76400,
She can swith her visa for a family member of an EU national.
To do this she will have to fill Application form EEA2 available from the homeoffice website or request one on the phone.
In this case your are the sponsor so you will need to prove your relationship(marriage ceertificate in your case) and proof of employment or self emplyment or self sufficient along with your passport and hers.
The whole application should be dealt with within 6 months.
this application is free.
One advice if i may : don't bother paying a sollicitor if you can provide the necessary documents.
here is the link for more info.
http://www.ukba.homeoffice.gov.uk/eucit ... ropeanlaw/
good luck