Question about parvo and stray dog?

I found a stray dog and she's a fully grown chihuahua. I know nothing about her medical history and if she's had shots or not. Should I ume she hasn't and give her a puppy shot? There was a parvo outbreak in our area a few months ago and I'd hate for her to get sick because she doesn't have immunity. Whould giving her a shot now, weaken her immunity and make her more susceptible or would it save her? I'm really confused and worried.