I'd look at the travel she's likely to do in the coming years, and use the miles whenever the paid ticket price for her trip(s) is expensive. For example, if she travels domestically, don't waste the miles on a $200 ticket, but if it's $500 or more, then pull the trigger. (If she travels internationally or in premium classes, the numbers will differ).

Also, since date changes are free on AA award tickets, use miles when plans are uncertain.

Finally, I think it's always a good idea to keep 25K in the bank, for when you have an last minute emergency need to travel on short notice when prices tend to be very high.