Herpes doesn't give you a single sore on the back of the hand. While it is possible (and very uncommon) to get herpes on the finger, it is blisters, not pimple-like sores.
If she used a condom while giving you a handjob, it wouldn't matter anyway. You're protected. Herpes would only affect the thin, moist skin on your genitals. The rest of your skin is too thick to penetrate.
Syphilis, like herpes, only infects the thin skin. If she had a syphilis rash, it would be on more than just her legs, and it wouldn't be skin color.
There is no risk here. You don't need to test, and there are no other scenarios you need to ask about. You're fine.