My mother went to college and got her masters in her 40s (she must not have complete faith in the imminence of armageddon) and it didn't take long to pay for itself in her case. It helped that she worked somewhere that helped with tuition, of course, but there are all sorts of ways to help pay for college that can help supplement things. It would be better to look at the field she's considering to determine ROI rather than just looking at "college vs no college" because there's a lot of kids that go to college and get a degree in history and are no better off financially for it.
Something else to consider would be to think about this beyond dollars/cents ROI - Personally I would consider returning to school once I retire purely for the pleasure of learning. If there's something that she's really passionate about learning, then even if it never pays for itself monetarily it may be worth the cost for the experience and the opportunity to work in a field that better suits her. If she's an exJW or otherwise has limited social support college can also be a great way to meet new people, have new experiences and make lifelong friends that have similar interests. A college professor of mine once said to the class, in the context of choosing a career, "money is almost never a good reason to do anything" and for most people who are in a good enough position that they're considering college as a possibility, I think he's probably right. Obviously if she's struggling to get by things might be different but if she can make it work and it will have a significant impact on her enjoyment of life, then who cares whether or not it pays for itself?