Hiya,
I'm a chick and I boat, I'm often the only girl and if not it's because I've dragged other girls along to keep me company. There's a few things I really want to say about girls and boating now all these are generalisations and so they won't be true all the time but there's probably some things that might help you help some female boaters.
First of all girls worry more about consequence than guys. If they don't have a solid roll, if the water's cold if the feature is munchy they are more likely to let this stop them giving it a go. Encouragement may help but patience is the main thing, let them take their time.
Girls won't put themselves forward the same way guys will, make sure that the girl in the eddy is taking her turn on a feature - it's easy for us to sit back and let guys push in it means we don't have to face the consequences (above). Some of the guys I paddled used to say "you have to take one turn for every two of mine" when I was started to play boat. Otherwise I would have just sat in the eddy.
On the same note, girls tend to underrate their ability. If you've sent an email round about a trip that might be good for some of the girls in your club then send them a personal one, just say "hey I think this trip will be good for you" - again they think about consequence and tend not to talk themselves up. I know several girls who wouldn't go on class III-IV trips on the club email because they felt they couldn't paddle class IV but in reality the boys that went were not even as good as them.
Girls get scared and yes every now and again we cry on a river. Boys never seem to know what to do when this happen but the best thing you can do is give moral support - comments like "you've paddled the hardest stuff it doesn't get any worse from now on" and HUGS help. A reminder that everyone has bad days on the river, a reminder that it's ok to be scared and a reminder that you can portage (assuming you can).
Encourage girls to lead - like playboating girls often sit back and let others lead and pick the lines. Make a conscious effort to put the girls in front every now and again. Let them take their time and don't let them back out unless they really really want to. Encourage rational thought process, ie. rational evaluation of the consequences - what's the worst thing that will happen here? A roll? A Swim? Sometimes fear is not in proportion to the dangers and it helps to discuss.
Anyway there's quite a few up and coming girls in my group now, and I encourage them as much as possible. In turn I get heaps of encouragement from the boys and the guys I paddle with are wonderful. I know some other girls that aren't so lucky, the boys exclude them from trips and don't acknowledge their ability.
As for relationships, don't teach your own girlfriend to paddle. If she's keen send her on a beginners course - she's less likely to blame her bruises, swims and fear on you plus she's more likely to listen to what she's told. But really, if shes only paddling for you it'll end in tears she's gotta love it or she won't enjoy it.
Just my two cents

Sarah