Receiver for entire house

It really depends on how this house is wired, and what she wants done. Assuming that each speaker location is wired with a separate volume control, and are wired directly back to a central location. Then, my guess is that you will need any decent receiver, but will require some sort of commercial amplifier to drive the load. Try doing a search on commercial amplifiers, or something like that to see what comes up.

It gets more complicated if you want any sort of control from these separate locations.

BTW, you might want to look at home intercom systems to see if that fits the need, or gives you any ideas.
http://www.mssystems.com/intercoms.html

Look at an impedance matching Niles box. They come in pairs up to (10?) pairs, which gives you up to (20?) speakers.

To drive this, you simply need sufficient power from any receiver or amp. The box's purpose is to prevent a safe load to the receiver no matter how many speakers are connected.

Note that some of the Niles boxes get quite pricey, and the one I saw that seemed to best fit her needs runs about $700. It's probably not trivial to impedance match that many speaker pairs.

As for power, if this person only wants background music, a receiver might suffice. Background music is only going to draw a few watts, and one assumes she won't have all the speakers turned on at the same time.

A pro amp for under $300 will give you 200 watts / channel. That would almost certainly suffice. Make sure the speaker box is rated for this.

I have never needed to deal with any such setup, so this is my best guess.

You might want to contact Niles directly if possible, or find a place which not only sells the boxes but understands them (good luck with that )

Also note, that you could run a more complicated setup using speaker zones. But I would not reccomend it for this person's needs.

You are better off going to the Home audio distribution forum for answers.

Popular choices will but the Russound products or the Nuvo Grand Concerto products.

Me, I use a extron audio switch to distribution digital audio or analog audio, 12 channel amp with volume controls, a PC (with CQC) and touch screens in every room. I control 8 rooms with this system (22 in-ceiling speakers), 3 full rooms of 5.1 sound (AVRs for those rooms)