All PDAs with user replaceable batteries have a backup battery that preserves the contents of memory when you change batteries. So don't take longer than 5 minutes to swap out the battery and you're safe. I think they say you can take as long as 20 or 30 minutes, but why tempt the fates?
You do not have to hold the record button down. Press the record button to begin a recording and press the stop button to end recording. It writes pretty much in real time (there is a buffer, hence a small amount of the recording is in RAM before being written to the card).
There is no external mic input, so she'll need to use the built-in mic.