There is no simple remedy for this. The best way to master this issue is to understand the conflict underlying the symptom. From what you said here, the conflict has as much to do with what you are thinking about her as it does about what she is thinking about you. Seeing a therapist is recommended. If you want to explore this before seeing a therapist, go to www.masteringstress.com and take the free stress quiz.
Your other alternative approach is anti-anxiety medication, like xanax, that can be taken right before the anticipated event, on a sporadic, and as needed, basis.
I used to have a similar problem where I would get sick if I have a presentation to give or simply meeting new people, so I started taken Xanax before the event and it seems to work just fine.
I had the same problem years ago. I would recommend Xanax as well. You probably don't need it all the time, just right before an event that causes you anxiety.