Just to add in my 2p again, because I can't help it
It's extremely helpful to have the person waiting for you at the airport, IMHO. I would be wandering around Birmingham at this moment if Steve hadn't come to pick me up and drive me back to Northampton--emotionally speaking at least, it's much less stressful to have a guide get you out of tricky situations even if you guys still end up taking a train or bus. Hehe, I found overall you'll end up relying on your SO for a *lot* of info, just where things are at, what shops to go to, what pubs are decent, etc.
The only reason Steve doesn't mind taking light rail when he's here is it's so bloody uncomplicated. Get on red line, take red line till it stops, call me, and I come and collect him. I'm not sure if it's that easy in the UK, we didn't embark on that adventure when I was there
I know she's really scared, but this might be the thing that gets her over her fear; her excitement will supercede her phobias, and it's something she might seriously want to look into if you guys plan on doing any US traveling in your long-term future