Hi, for the most part from what your describing, any syphilis contraction would appear on your penis not your upper mouth. You can take a syphilis test if that would ease your mind but what your describing doesnot indicate that you contracted syphilis.
"Exploding" is a relative term. Yes, it is rising, but this shows you the rise over several years in France - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6386212/#!po=34.3750 So while infections have risen dramatically, it was still less than 1,500 cases in 2016 (the last year I could find stats for - if you're in France, you might have easier access to stats than I did). You can also see the populations that have most of the infections in France.
She gave you oral sex, so if you got syphilis from her, you'd have genital symptoms. Syphilis isn't spread by kissing.
If you are concerned, just get a syphilis test. It's a simple blood test. I'd be surprised if it was positive, though.