As a landlord, I can assure you, that even if one would use 100% financing on a $24K property, have to do a ton of work on it, and then rent it out for $700/month, that person would do freakishly well with that piece of property (and that is without knowing a single thing about the neighborhood or value of the house). She split it and paid cash for it with her mother, who is going to gradually be bought out... With the kind of cash flow that this thing will provide her, it won't take her too long either.
As a side note, I totally relate to her being a landlord that is younger than the tenants that she rents to; in my experience, it will occasionally make for some very odd interactions. I wish Willow nothing but the best in her landlording and business ventures. If the NPR story is indicative of her as a person, she is a lot smarter than I am and I look forward to someday reading about her on the home page of the Wall Street Journal.
Disclosure/Disclaimer: I am long various types of real estate, but do have a few houses for sale... This is not advice of any kind. Always do a ton of your own research before contemplating doing anything that I say, do, write, or so much as think about.