Its hard to watch it happen :(

How about using epoxy to put caps over the buttons she doesn't need?
We did that with a radio for our son when he was old enough to
understand on/off and volume but didn't yet need all the CD management
functions on what was at the time the simplest boombox we could find.

+++++++++++++

Reply to the list as I do not publish an email address to USENET.
This practice has cut my spam by more than 95%.  
Of course, I did have to abandon a perfectly good email account...

Take a look at shower radios; for instance, search http://www.target.com
for "Jensen shower radio" or "JMW125"

1.  We have a cassette player/radio.  It has a switch marked
"tape/radio".  When you toggle to "radio", the radio comes on, with
whatever volume and station were used last.  The "tape" option basically
means "off".  The tape plays when you put in a tape and press the "play"
button.  If you took the knobs and switches off, or just put duct tape
over them, it will just leave whatever.

2.  My house (and many others) have one or more outlets controlled by a
wall switch.  These are intended for lights, but if you have one that
isn't being used, you could plug in a radio and it would be controlled
by that switch.  By putting the radio on the floor or on a shelf
somewhere, your mother wouldn't have to deal with the controls.

3.  Back when my father still had his memory, he was still a little,
well, whatever.  He had a radio in the kitchen.  Rather than deal with
the controls, he bought a little switch.  I have one myself, and they
are really cheap (US$1.00 ?).  There was a wall outlet above the kitchen
table, and he plugged this switch in.  The radio was then plugged in to
the switch.  It was a toggle switch similar to what is used to control
lights in the house.

4.  I have a light in the living room.  The switch stopped working, and
I just removed it.  I plugged the light into a power strip and put it on
the edge of my computer desk.  The power strip has an on/off rocker
switch.

We bought my 87 yo aunt a cassette player in a toy store to get really big
and simple controls.  Maybe they have radios also?

I would buy a table radio.  A cheap one.  With knobs. Tune it to the right
station and pull all the knobs off except the volume/on-off.  A modern
radio with buttons wouldn't be so easy to modify, though as someone suggested
with enough epoxy you can disable most anything.

I would look at thrift/second hand/Salvation Army/Goodwill stores and
garage sales.

Sony used to make an ICF-9740F that was pretty
good and had knobs but I think it is out of production.  
Probably shows up on ebay.

A good place for cheap radios [table &| clock] is

http://www.jr.com/

Also amazon.com and ebay.