There's a couple things here:
1 - that sensation of having to urinate is 100% normal.
2 - make sure to tell her that it's 100% normal.
3 - have her urinate before sex play, this will help reduce those sensations
4 - if she happens to expel fluids during orgasm there's an overwhelming chance it's *NOT* urine. Women ejaculate too! And it comes from the same place as urine; just the same as men.
I'd get her some sex toys and encourage masturbation as well as encourage her to read up on orgasms. Often knowing more about it will help. I also agree with having her watch you orgasm; perhaps you could masturbate to orgasm now and again for her.
Here's a few other media:
orgasm every day
exploring the o
orgasms
celebrating orgasms
It's great to see that she has such a dedicated and respectful and communicative partner!
I'm sure she will be orgasming in no time! ^^
Oh, one other thing: make sure she knows that there's NO WRONG WAY TO ORGASM! Every woman is different in their orgasms. Some are wild and buck around screaming, some are soft and quiet. Some, myself included can be both. I've been known to scream, swear, kick and hit, and I've ever cried during orgasm before. I'm more wild during sex, and more quiet and calm during masturbation.