Yes acne can still occur at the age of 31. It can also be a symptom of PCOS (as well as the irritability, but some women simply have more severe PMS than others). If she was on certain birth control meds it could have suppressed the acne before and when she stopped taking them caused her to break out.

Of note: a blood test that was done 7 years ago doesn’t say much about today. It is just a reflection of what her hormone levels were at the time.