...we're looking for a solution that fits those varied parameters, which may include buying a little acoustic guitar amp, maybe a pedal of some sort to get the best tone, and definitely a better guitar for her as she currently plays with an inexpensive Fender acoustic that we had to glue the headstock back on recently.
My best guesses based on the needs you laid out...
Little acoustic amp: I recommend those green Crate amps. They're still making those, right? They're pretty inexpensive and come in all sorts of sizes. Just make sure you get one that's powerful enough for your needs. I played in a rock band with someone that had the 30 watt one and it was woefully inadequate, but a bigger one would have been just fine.
Pedal of some sort: I love my Baggs Para DI. Other than that, I don't like to get too crazy with pedals on acoustic.
A better guitar: My personal opinion is that great plugged-in tone on acoustic starts with great unplugged tone. Some guitars come with great electronics built in, but a lot don't, especially in lower price ranges. Beyond that, it's all about your price range. Have Julie try out as many guitars as possible, because ultimately what sounds/feels best to her is most important.