My general rule of thumb is that unless you're flying at least 25,000 miles per year, the cost of remaining loyal to a single carrier probably outweighs that of the eventual reward.

Say the cheapest flight on your mom's usual route is $800 via Air Anybody, but she spends an extra $200 to fly AC because she gets miles for it. You said she flies about 12,000 miles per year... I don't know how many return trips that is, but let's say two. So to stay loyal, she's spending $400 more than she needs to each year. She is racking up 12,000 miles per year plus 10,000 miles from credit card use, or 22,000 total. Perhaps the credit card annual fee is $75. That's $475 / year in unnecessary spending.

If an award ticket costs 50,000 miles and it takes Mom 2.5 years to compile 50,000 miles, she is theoretically spending $1200 in pursuit of a prize worth $800. Smart money says she should have just flown as cheaply as possible with Air Anybody in the first place, and forgotten about the miles.

Your figures will vary, of course, but think along those lines. The math is pretty gloomy for sub-25k flyers trying to make these programs work to their advantage.

And of course, as you probably know, the FF programs are getting more and more dilute... redemption is harder, and costs more miles -- making them of genuine value to fewer and fewer people, especially occasional flyers like Mom.