I’d pick something with more steam than a poodle shooter if I was thinking about a meet up with a bear.
While I initially have the same thought bigger is better if concerned about Alaskan Brown Bear, the reality in such a situation is going to make shot placement and ability to control far more important. A rifle she accurately shoots with will be your best choice.
Alaska Department of Fish and Game
Firearms and Ammunition
http://www.adfg.alaska.gov/index.cfm?adfg=hunting.firearms