Traning and potty training advise

So I was given a doberman puppy in December. She is roughly six months old. When I got her she didn't know anything and wasn't potty trained I had her for over a month now and she can only sit when there is treats involved and no distractions. I've been trying to potty train her but she's still going potty in the house even though I take her outside to go potty. This is my very first Doberman and very thing else other training skills I used for all my other dogs doesn't work on her. I have started to do my research and trying ways I see YouTube on how to train a doberman but still nothing worked. I have really nothing for background beside she was updated on vaccines but they never sent over shot records. She was supposly to be around 18 weeks when I got her December 23rd but the Akc Paper for the date is August 23rd. She was very skittish and was in a cage with 3 other dogs. But she was one of the ones that never was adopted. The dude said he was selling all the dogs he was breeding dude to him getting divorced and the other dude that was with him lost some records. So I have no idea of previous living conditions or linage of the parents or nothing so i do habe appointments with vets as well as getting a hold of the Akc to see if i can get more information about her. If anyone can give me advice on training her I would be super grateful .