It's possible. A sore can be caused by a lot of different things - syphilis, herpes, friction, infected hair follicles, clogged oil glands, etc. Does her sore hurt? A syphilis sore is painless.
If you haven't had a sore, it makes it less likely that you've infected your partner with syphilis, . A syphilis chancre can appear as early as 10 days, but the average is 3 weeks.
Is your partner going to the doctor? She should - it could be anything, including something not an STD that still may need treatment.
It's worth a test for you, but it's still pretty early for you to test positive if you have it. That can take up to 6 weeks. It wouldn't hurt to test now, though. Let us know what happens.