Try Girl Power in the Inner Thoughts section.

Anabelle

Ever take into consideration the reason she knows how it is done when you do it, is because she knew how it was done before you did it? I.E. that she might have studied the art of magic at some point.

You've created an impossible situation for yourself. From now on nothing you do for her will be magic, it will simply be puzzles for her to try and figure out.. If you do fool her, she won't believe in the magic, she'll just be frustrated when you won't show her a second time. (because she's certain she'd catch you that time!)
Is this the relationship you want with your audience? I would try to remedy this by shifting your emphasis to entertainment. Try a trick such as Sam the Bellhop that has a very strong emphasis on entertainment, and try and show her why magic is enjoyable.

I second geoff weber's oppinion. everything is a challenge to her now.
it is all about catching you "red handed" .
I don't know what you can do to fix this. so I would go with geoff weber's advice.
good luck man !

-Matt

Try doing something with a memorized deck. If she does not know you are using one, you'll fool her a big time. That's a beauty of the MD, the effects are very strong and escape any logical explanation unless you know the MD is used.

Holy grail - card at any number - its a kicker

lol

Recently I found a friend who I had never performed magic for before, and I'm pretty certain has never studied magic (im pretty sure I'm the only one in my district). He claimed he could see through most magic tricks, that he didn't really care if he didn't. Of course, I was curious and decided to perform the invincible mindbender. He didn't have a reaction at first, so I assumed he didn't see the bend. when I pointed it out, he said "so what?" and proceeded to give me the scientific rundown of how he thought the trick worked. He explained it better than the creator. Now, I set up for the trick when no one was watching, and my performance wasn't majorly flawed in any way. I think theres just those kinds of people out there.

I find that if a person is absolutely fixated on HOW a trick is done, I have failed to provide an ENTERTAINING PRESENTATION of the effect. If the trick is being presented as a puzzle, then it's not surprising that she feels challenged to figure out how it works. Not having witnessed the presentation of the effects, it's really hard to say what the cause may be.

Regardless, you need to shift your focus. Assuming your technique is good, try to entertain instead of fooling the spectators. Solid entertainment is the best form of misdirection.

Kent

I think Geoff and Kent are right on when they say your focus should be on entertainment. The best approach might be to put a comedic twist on things. If you get her laughing, she'll be having too much fun to worry about how the effects work.
Besides, the #1 thing women always say they love about a man is 'he makes me laugh'.

I think your purpose of showing her magic, and her purpose of figuring out your tricks are the same. You want to impress eachother. Put the cards away and invite her out instead.

Michael

Thank you very much for all the good advices, but I discover her secret, when she was young she read a magic book, since then she has developed a king of "eye" for magic, however I fool her with the arm twistling illusion but no way to fool her with any mentalism stuff. I know try to fool somebody in this way is not exactly "magic", but I don't think that to do magic you have to make people "belive". Probably the best approach is a funny presentation, at the end is what people always remember more than the trick. I will work on that.