This statement acknowledges that brave and strong women can find themselves in relationships with individuals who may lack courage or display cowardice.
"It's not your fault sometimes brave women fall in love with cowards" suggests that the woman being referred to may have been attracted to someone who does not possess the same level of bravery or strength.
The phrase implies that the woman's bravery and courage may have led her to take risks or be vulnerable in love, even with someone who may not reciprocate those qualities.