Is it possible for a woman to know if she's infertile before she ever tries to have a baby?

Sometimes. If medical history indicates a problem with ovulation (e.G infrequent cycles), tubal factor (history of pid) or male factor (e.G vasectomy) otherwise fertility potential can only be deciphered by fertility tests.Another point; consulting with a fertility specialist will notonly address fertility potential but also the safety of getting pregnant through preconception counseling, genetic screening ..
Rarely. Rarely a woman has major problems like never starting her periods or not going through normal puberty, and may not be fertile. Some women start their periods then have no periods later (secondary amenorrhea), but this is usually subfertility rather than infertility. Most women with subfertility/ infertility don't know it ahead of time. Conversely some young people wrongly think they're infertile.
No. In a women who has no known reproductive abnormalities, it is difficult to tell with certainty that she is completely infertile. If a couple has trouble concieving, they should seek evaluation and treatment from a specialist. Many identifiable fertility issues can be overcome.