My wife have a Rubella IgG result shows 45.14 IU/mL (Positive). But she has not vaccinated rubella. Right now she is pregnent of 25 weeks crossed...

Normal. A test for Rubella IgG tells us whether she is immune to this virus - with a "high titer" or 45, this tells us she is immune to Rubella. Since she was not vaccinated, this tells us that she had the infection in the past; however, this should not pose a risk to the fetus. Consult with your obstetrician about these results, but from this alone, there should be no cause for concern.