Pooping in the house (no pee)

Hi, I am sure I am jumping the gun here but I just got a Lab and Hound mix from the APL. She is a great pup who is about 3 months old. The main problem I am having is that she poops in the house and will urinate outside. After a few days this still persits. I also have 2 othe rolder dogs ( a Black Lab 13, and a Boxer 5). When Ginger, the pup, goes outside I give her a ton of priase and reward with a treat when she comes in. I have found that the praise doesn't seem to be doing much as she ignores it and moves on.

Like I said, I feel that I am jumoping the gun here because at this point she really doesn'e even know her name. Its been 13 years since I have had a puppy to housebreak.

Any help would be very much appreciated.