If you're going to ask speculative "what if" questions, you could go a lot farther than syphilis. Chlamydia? Gonorrhea? Herpes? (Herpes is the major STD risk for HIV transmission.) What if she actually has HIV? And isn't taking antiretroviral therapy?
You can play that game all you want. The important thing is that nobody has ever been proved to acquire HIV by the exposures you describe. The chance she had syphilis, or that you acquired it, is just as low as HIV. You don't need testing for either infection unless, as you say, you develop symptoms that concern you.
HHH, MD
Thanks
I will not post another question after this.
HHH, MD