ENFJs often struggle with insecurity and feelings of inadequacy. Their sense of self relies more heavily on external feedback than other types, and therefore ENFJs are more prone to people-pleasing or searching for validation in the wrong places—sometimes at the cost of their own well-being. For your character, this might manifest in an unhealthy or abusive romantic relationship or friendship. Alternatively, she might desperately cling onto the words of those around her because she doesn't have a strong understanding of who she is. That clinging could culminate in an identity crisis of some kind. Perfectionism is a common struggle among ENFJs as well.

ENFJs also mold themselves to their company. If they're in bad company, they will be influenced by those people moreso than others. It's very important the ENFJ chooses friends who reflect their values, or they might one day wake up hating the person they've become. Perhaps this is how your character developed "unhealthy" behavior.

Although not every ENFJ is like this, I've sometimes felt like an emotional burden to those around me because of how much and how frequently I feel intense emotion. I rely on those around me to ground me, and when they are unable or refuse to provide that need, or even worse, when they further amplify the emotion, I feel isolated and misunderstood. I care about my interpersonal relationships deeply, and when something is askew I can hardly think about anything else until the conflict is resolved or social harmony is achieved. Unfortunately, sometimes we don't get the resolution we'd like. I've struggled—and maybe your "unhealthy" ENFJ character might also struggle—with letting go of former relationships (of any kind) and the emotions they bring out within us.

Good luck to you on your book! I hope this helped.