Dawes touring bikes are very good, especially the steel ones. Alu is lighter but tends to transmit vibration and road 'buzz' more than other materials. Your daughter may be okay with this - lots of people are - though I myself can't stand it. Steel forks may help with that a little?
Of the 43 and 48, the 48 sounds promising. Quite a lot can be done to optimise fit, e.g. different stem and/or handlebars, as no doubt you know. She should probably try the 43 too before deciding, just in case that feels better and/or the component swaps needed to make it fit are easier/cheaper than what might need swapping out on the 48.
I don't know what stock saddles Dawes uses. Do you have a link? Saddle comfort is very individual. She may like the stock saddle. Again, it's one of those things that needs to be tried out, with a realistic expectation of perhaps trying several more before finding one that works for her. Again, the sooner she can get started putting time in on the bike, the more time she'll have to get these questions settled and the right stuff bedded in before the big trip.
Same goes for gear for the weather conditions and gear...! I'm happy to talk with her about this, but not via an intermediary, that would take ages - sorry!
Meanwhile - has she got cycling friends she can discuss all this with locally?
If not, I'll PM you my mobile number, but there's only so much anyone else can do on her behalf... whether it's before she gets a bike or after, the sooner she starts going round the shops, reading online threads and asking questions herself AND meeting people, the better.
Winter is a good time to get this process started. 
And my previous recommendation of YACF still stands!

ETA: I know costs are a concern. If your daughter gets to chatting with people on YACF, I am sure she will find some who are willing to lend her things to try out. I know I would be, if, after talking with her, it sounded like anything I have that's not currently in use might be useful to her....
Last edited by Rebecca19804; 12-04-2011 at 11:31 AM.
Rebecca
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