My D is an Econ major at an LAC and is graduating in three years, in May 2019. Having watched her through this decision process i I would look at what your D has done and accomplished already, what she intends to do after graduation, and how another year in school might affect her plans. What does her resume look like now? What will she do this summer? Will she have an internship in her field or an REU, or would she be entering the job market with no experience if she graduates early? Could she study abroad and gain some intercultural experience next fall? What additional coursework would make her better prepared for what she will do next? Is she ready to leave school and enter the job market or could she use a little more time to mature or whatever?
In my kid’s case, she’s basically maxed out what she can do by staying in school. She studied abroad twice, did an REU, has work experience and an internship, has nearly enough credits for a double major but it’s the coursework, not the second degree that will help her, and she has a great job lined up and grad school plans for the future. At times it felt rushed, or like she could have had an easier time by adding a semester or a year, but it would have been costly as well. It’s not that there’s no value in staying, but for her it makes more sense to go, and she is quite ready to do so. I think if last summer had not had the REU or a solid internship, more time to add some sort of meaningful experience would have been a good idea.
Good luck to your daughter as she thinks it through.