Wow, sorry for the delay coming back to this. Thanks for all the replies!!
To ido1957 - that is what I was trying to do - insert an outboard compressor - but the signal chain is: voice-mic-interface (no insert - just a Fast Track) - computer. There isn't anywhere obvious to put a compressor without getting a separate pre, which sounds like an awesome idea actually. I might try that. Also - there were some excellent ideas about using two mics (though room sound difference might be an issue) and/or having multiple takes at different levels.
Mic technique is great but it's just one more thing for her to worry about while recording. Some of the music is pop with VERY large dynamic range. One of her songs is reminiscent of Avril Lavigne and Alanis Morrisette with very soft verses and then explosively loud, full-voice belting for the choruses. But I think with some combination of the advice you've given me, we can make things work now.
Thanks again!
Ryan