I'm in the same situation as you regarding skate shops, my closest is 5 hours away, the better one is closer to 8; the tech I trust the most is out of the country. It's a real conundrum and pain in the bum. We have young kids so choose to make a family trip out of it and play the tourist. I agree with what Amy above says- start with the Kinzies closet size charts and do all those measurements. That's a great start. However it's no replacement for advice from a seasoned expert.
Here's how I handle skate buying, take what you will from it. First, I make sure I'm going to the most knowledgeable and trusted skate tech, even if it's further than the closest. My logic is, if I have to make a weekend of it anyway, I want to have the best resources available. I did this by asking around the rink and on forums (I'm in France, so had the added joy of language issues). Then, I called ahead and made an appointment and also explained my skating level, personal fitting issues (again, to the best of my ability), and particular boot models I was interested in. They asked me my size, and when I did arrive had a nice pile of boots for me to try on. I was able to hit the ground running once I got to the store.
If she's got "weird" feet, and many of us do, you may be in a situation that requires semi- or even full customs. You definitely want a skate tech's help with that. There is one woman on these forums who has skates that are not only split width, but also split length. There are a lot of possibilities out there without needing to go the full custom route/pricetag.
Good luck with this. Buying skates is hard enough without these extra challenges.