What that effectively means is that a NEGATIVE INCOME (read LOSS) on SCH C occurs every year -- A KNOWN RED FLAG.   

I imagine different lenders/underwriters would have different policies on the matter, but I'm hoping they'd view the HELOC similar to a credit card (zero balance = zero effect on your DTI) as opposed to a car loan (which is a debt for which the monthly payment would definitely be factored into your DTI). 

She may not want the landlord to come back and say she is late using a bank posted date which could be days after rent was delivered to the landlord or something to this effect.  

Alternatively mail to them but I think calling is more effective.

Late payments can have a big effect on your score as well.One way to get into real estate investing is to house hack.

Hey - the red flag right away is that the listing appears to confuse effective rents with net operating income.  

The lease is still in effect and you will be tied to the terms of the lease during this period, if you are lucky enough to be month to month, then the lease is terminated after the last month paid for by the tenant.  

What is the cheapest and most effective ways to direct mail ?

I would be confident your strategy is effective before you start scaling your marketing budget.

Building a website yourself is going to be more cost-effective and ultimately more efficient.