ALT can be high for other reasons. Muscle damage, heart damage. There are several places in the body that manufacture that enzyme. There are many tests that go with high liver enzymes. autoimmune hepatitis and celiac's diasease are the ones I remember. Might also be due to taking several over-the-counter drugs which can harm liver or from drinking.
Have them repeat the hcv screening test so you can stop worrying about it.
What hope said, get both tests done again. Mistakes do happen.
oh and i should have mentioned that the rna test may also give false results, so her doctor should run both again.
it seems likely that your gf was exposed to hcv at some stage, although the antibody test should be redone as the can give both false negative and possatives, some people can clear the virus from their systems but will always have antibodies in there blood afterwards. it is also possible that your gf did become infected and her body cleared the virus brom the blood cells that are normally tested but it could still be present in pmbc blood cells (at least thats what i think they are called) or they virus could still be present in her liver or other tissues. if so this is called occult hcv infection, which appears to be a less nasty form and only recently discovered type of infection. if you search occult hep c on the net you ll find some info. it was thought that the lucky people who could clear the virus by themselves where completely virus free, but recently new evidence has emerged to suggest that at least some still harbour this occult infection. hope this was of some help.