Your doctor should investigate the issue.
A slight elevation can be illness or thyroid or many many other issues - so it should be tested over time.
A slight elevation though, in me, was a tumor... so it can vary in people. But I was fully lactating too. Is she having sore breasts at all times? Irregular periods can be so many issues - but if they toss BCP (birth control) at her... IMHO, it may not help, for instance it did not regulate me which should have been a hint HINT! but instead it was more of a blame game...
I also had many female issues such as PCOS and endometriosis concurrently with my pituitary issues - this can muddy the waters for diagnosis. A lot of us do.
All the other test came back accept the prolactin..The lab normal range was 20 my daughters came back at 22..
Every lab differs. So you have to know the lab and the range.
Hopefully the doctor did more than just prolactin - as in thyroid (thyroid can raise prolactin) and androgens (male and female hormones).