Found a long haired Chihuahua that I believe has been abandoned. What's the best way to potty train?

Ok so there is a long haired Chihuahua that has been roaming the streets for weeks and I believe it was abandoned. She has obviously been a mother before because she has hanging nipples. No idea how old she is. I decided to take the dog in but I'm sure it was originally an outside dog. How do I go about potty training her? I've never really had an inside dog before besides a trained weenie dog my wife had before we met. Any advice? I just brought her in and gave her a flea bath.

Thank you in advance.