Interesting situation that I am analyzing and could use some ad(vice), questions, discussions to help me flush out the nuances of the two options.

Listen for awhile after the flush.

I don't know if I would put this in the 'Top 5' mistakes, but leaving a weak flushing toliet in a rental property is a really bad idea.

I am a big fan of the Fluidmaster complete toilet rebuild kit (about 20-30 bucks) if the toilet is otherwise sound and not cosmetically flawed.The HD page: http://www.homedepot.com/p/Complete-Toilet-Repair-...This kit replaces all the seals, fill valve, flush valve, flapper, handle, bolts, etc. 

I have literally had a full bath completed, paid an after work completion permit, had the inspector walk in and flush the toilet, and then walk out...In downtown Seattle, that one toilet flush costs $600...there are times its ridiculous.

This is a flushing agent that causes the roaches to flush from their hiding places, run into the freshly sprayed chemical (I always prefered the chemical Demand CS with an active ingredient of Lambda-Cyhalothrin)It may take 2 or even 3 treatments to eradicate the problem and is not cheap if done right.

(And this one is a real pro tip because it almost always flushes out these scammers.) 

In that case, I would tell her that she can find the answers to even the stupidest questions, including how to flush a toilet http://www.passionateamerica.com/idiot-proof-guide-how-to-flush-a-toilet/ by searching on Google.

Sometimes there is no clear case of "cause".Plumbing is always a tough one.If you have a obstructed branch line because a tenant's kid flushed a rubber duck down the toilet, but it would have made it through if the pipe were not partially obstructed by tree roots. 

But don't miss the forest for the trees if you've got older toilets or those that may be "low flow" but perform so poorly, they require multiple flushings.