I think that after a certain point, the parent should step away and let the adult child be accountable to a professional. It's ok when the kid is 16, or 18, or early 20s, and dealing with life's business for the first time. That's when teaching happens (how to fill out a rental application, how to apply for a loan, how to balance a checkbook, how to get insurance, etc).
But if financial irresponsibility, or addictive behaviors, or social media blunders, or employment problems, or personal hygiene/poor housekeeping issues persist until the adult child is way past his/her mid-twenties, into his/her thirties, and now, like your child, when they're nearly 40, it's time to help them find professional guidance.
It sounds as though your daughter has developed some really bad habits when it comes to organization of finances, and she hasn't listened to you up till now, and she's probably not going to listen to you at this point. Teaching time is over.
A financial counselor can help her refinance her student loans, and provide her with the tools she needs to get control of her life. I wouldn't offer any assistance other than, if it's possible, paying for a session with a financial planner, and perhaps even going with her if she's hesitant or fearful or reluctant. But don't step in and straighten her life out yourself. Make her accountable to a professional.