I'm starting to parse through the discrepancy in the different rules of thumbs I've been introduced to by others, thanks for you comments and clarity, Jon.
I've seen numbers that a home MIGHT make financial sense after @ 15 years, before that, renting is often better. And if you splurge on a McMansion, or pay high rates, it might never make sense. I view a home as a lifestyle decision, more than an investment (for the avg. person - and eventually for me).
But this means that my friend is actually coming out ahead when she has someone paying most of the expenses of her property, even though she doesn't make it to the 50% rule. Through appreciation, keeping up the property and inflation pushing up rents, she'll have an income stream, and an asset worth more than what she put into it.
So, she is likely going to make money, but we could question the return on equity (down payment, other expenses along the way). Maybe the return isn't great - but probably annuity-like. If she gets a lot of appreciation, then the numbers might look quite nice.
So is the 50% rule a business rule, rather than an investing rule? If someone is running a RE business, they need positive cash flow, whereas an investor needs a place to put their cash, and a real return, hopefully something better than T bills?
Does this make any sense?