[Coda]

The problem isn't distance; it's SNR (signal-to-noise ratio). Distance (including barriers) is one of the most common CAUSES of bad SNR, but a weak transmitter will also cause the same problem. And while a wifi extender will improve signal attenuation due to distance or barriers, it doesn't help when the signal is weak because it was never powerful enough to begin with.

Now, it's possible that a repeater might be able to do the job for you anyway, if its transmitter is more powerful than the one in the router. At that point you could just plug it in RIGHT BESIDE the router and get an improvement.

You might be able to convince your mom to buy this one by pointing to the fact that it calls itself a "range extender": https://www.amazon.com/Securifi-Almo...n%3A4676750011

Or this one, because it labels itself a "wifi booster": https://www.amazon.com/D-Link-DAP-15...n%3A4676750011

Or this one, which is specifically labeled a "repeater and range extender": https://www.amazon.com/StarTech-Wire...676750011&th=1