Dave Ramsey is way off base here IMO.
First of all, he provides no reason for why a person should have to clear 100% of a debt before taking on further debt. Why not? This is some hard and fast rule he lays out like it is the law, but he gives no supporting argument for it.
As some previous posters pointed out, there is simply no reason that she and her husband should have to rent instead of purchase. If they plan to stay in the market and the market has good future growth potential then why shouldn't they buy a home? Don't go crazy and buy a mcmansion, but you are going to be spending money on a rental anyway so why not get equity out of it? Ramsey is oversimplifying things here and the patriarchal tone is pretty condescending to my ears.
This reminds me of his snowball method for tackling debt, which, if you are good with money, is actually a terrible idea. As I understand it, he suggests that you list your debts from least to most. So for example:
$5,000; $50,000; $70,000
Pay off the smallest one first according to Ramsey.
Bad idea! It may be great advice for your average Joe who gets psychological satisfaction from eliminating a loan quickly, but it fails to take interest rates into account. What if the $5,000 loan has a 3% interest rate, the $50k loan has 5%, and the $70k loan has 8.5%. You would be a fool not to put every dollar you can towards the loan with the highest interest rate first while making minimum payments on the other two!
Furthermore, his assertion that you should pay off your existing debt first is completely misguided for those of us who will manage to refinance our loans after graduation. Most financial types these days suggest paying the minimum on the loans if the interest rates are lower than ROI on the markets and then put whatever money you would have paid towards the loans into the markets for your retirement and savings. Why would you put $40,000 against a student loan at 3.5% interest if you could put that $40,000 into the market with an expected 7-8% return over the long-term? That is just bad advice.
If you are a dentist with $480k in debt making $120k per year and you want to buy into a practice, Ramsey would say that you should pay your debt off first, but that could be very costly if you would be buying into a practice with significant income potential. My fiancee has to buy into a surgical practice after she's made a partner and it will be expensive up front. But within 3 or 4 years she will break even on the investment and from there it is pure profit from ancillary (passive) income. She will be taking out more loans on top of existing loans, and yet it would be absolutely foolish not to and miss out on years of passive income.
Running a business, being good with money, it requires you to take calculated risks and to know how to manage your debt. Debt is not your enemy if you can manage it well.