So my girlfriend and I had sex when it was 5 days post ovulation, what are the chances of her getting pregnant? Are they high?

Not high but not 0. If you knew the moment of ovulation, Pregnancy risk would be low in 5 days. The problem is that the timing of ovulation is quite variable. It doesn't happen exactly when the app says it will. Trying to prevent pregnancy by timing ovulation is notoriously unsuccessful. Best to assume pregnancy is possible any time you have intercourse. Risk is lower but no zero. Best wishes!