My wife had a Geo Prism. It's the same car. When we bought a van and moved to Virginia, the van became hers and the Prism was mine . . . until 2008 or 2009 when she took my son to a music lesson and someone T-boned the Prism, totalling it. That's when I bought the Silverado.
And your girlfriend is right. It's an extremely reliable car, though I don't know if they're made as well today. What I will say is that, new, the Corolla was about $2,000 more than the Prism. Since the only differences between two were the hubcaps and the trunk hood - the two cars were even made at the same factory - it's apiparent that some folks will pay $2,000 to have TOYOTA's hood ornament instead GEO's.
I will say this: Prisms and Corollas both have the crappiest paint jobs of any car I know. Half the paint flaked away on that Prism. Every so often, I see something with the same screwed up paint and it always turns out to be a Corolla or Prism!
That wouldn't stop me from buying a Corolla, but it does make me wonder just a little about Toyota's quality control.
The photo below isn't my Prism, but it's exactly what happeened to me and bunch of other Prism/Corolla owners. (How is your girlfriend's paint holding up?)