This is a tough ethical dillema and I'd like to start by stating that I feel the same way about wanted to be noticed by your nurse. Generally women often in my dealings seem to encourage this to a certain degree as I used to wear loose clothing and pajama pants to my chiropracto's appointment to have the same thing happen. On the day that I wore pajamas, probably the most revealing, she sort of threw in the comment "these appointments seem to get better and better everytime." This was when I was on my back and my dick started throbbing a bit at the implications of the situation. Another chiropractor said "we all want what we don't have" out of the blue just as she was flipping me over. I'm pretty sure she could sense I was marginally aroused and almost expected her to make things a bit sexual.
As far as her becoming upset with your actions, you have to consider this a possibility, and not a probability. As long as your not a freakish horndog about it in my dealings women are very open to men who are unashamed of there sexual feelings/curiosity so long as it is not crossing any major lines and you're sensitive to the situation.
Not to mention I also know that a good deal of women appreciate being noticed. Of course it has to be in the right way and not come off as creepy or like grabby.
One issue is that women are different in these regards. Men, would love a sexy stranger to become as aroused as them and bang right there. Women generally prefer to know a person and a random stranger no matter how good looking/powerful/wealthy, could actually inspire disgust by being to overly generous with his looks and for any reading this feel free to comment on this.
As far as her telling you she would not be able to treat you, I think as long as you don't bash it to death and are like "I'm getting this hard on, and she is going to notice it" (as that would creep them out certainly) this would'nt be an issue. This isn't a recurring issue and it's not like you're forcing yourself on her. But it's still given that you don't know where she is at sexually/relationally, this is something you can't overrule.
All in all, maybe you should just feel it out and go for it. That is if you weren't married I would say that. Since you are married I think you should focus more on controlling your desires in the moment and focus even more on having fun with the situation and connect with her on a different level. It could end up that you make new female friend or group of friends! If your not typically "the social man" your wife might find this a refreshing thing too.
But who knows that's just my opinion. Let me know what you think and maybe we can talk more about this.