You must try the FART test to see if she is a "keeper".*
If you go out in the car for a drive to some romantic spot then as you get about ten miles away from home let out a massive rip-snorting FAAAART. If you can get it to change tone part-way through then that is perfect. A two-tone five second long loud fart.
It needs to start loud and low then reach a crescendo in a kind of squeak at the end.
Obviously it will take a few seconds for the aroma to reach her nostrils. The smellier the better. Rich and memorable is what you are aiming for.
Is she a keeper?
If she doesn't vomit she's a keeper.
If she doesn't get out the car ten miles from home she's a keeper.
If she goes out on a second date she's definitely a keeper!
Hope that helps!
*No underpants were harmed in the making of this post.