Potty training a 6 month old chihuahua?

I was given a 6 month old chihuahua and the previous owner allowed the dog to pee on potty pads instead of teaching it to go outside.So now I am trying to re-teach the her but am getting very frustrated.I will take her out with my other dog Bootsy so she can see her go potty outside.We will walk around for 15-20 mins(on a leash) and nothing will happen.Then no more than 10-15 mins.after we get back inside she will go potty on the carpet.I have no clue how to go about re-training her...HELP!!..does anyone have any good ideas??..Thank you.