Great Dane won't leave condo for walk

Please help my Dane won't leave my condo. I recently adopted a 2 year old Great Dane. She is a sweet girl and kind and gentle. Her first night here I took her for a walk after our car ride home. That went well except she pulled me. I made the mistake of not crating her while I washed dishes and she pooped on the floor. Later that night I took her out before bed and she freaked out. In order to get out of my building you must either use the stairs or elevator. I chose the elevator bc we'd used it earlier. When the door to the elevator opened she immediately ran in the other direction pulling me with her but got on the elevator anyway. When exiting the elevator she got frightened by another dog's bark and scrambled down the hall pulling me to the ground. At this point I probably should've just went back to the condo but I continued and took her outside where she was fine until we were approaching the entrance. She froze and started to pull in the other direction. I remembered I had treats in my car so I went to get them to see if I could lure her back in, that was a HUGE mistake. She got in the drivers seat and wouldnt budge, I had to pull her out of the car and I feel terrible about it but I felt like she wouldnt have come on her own. We make it to the door where she becomes visibly anxious so I calm her down and im able to bring her back up. This happened 4 days ago and since then she won't move once I put a leash on her. I've tried the easy walk harness but it didn't help her pulling so now I have the halti head harness. She lets me put it on and she doesn't claw at it and she isn't able to pull me but she gets to a certain point where she just stops and won't move. I know I shouldnt pull her because it'll just make her pull back. What can I do to help her go outside. I'm getting nervous that she will never feel safe enough to go out. She isn't able to get the exercise she needs so she whines at night when I crate her. The whining is getting better but the not walking is what worries me. Also My entire living room is covered in puppy pads. Is there anyway to teach her to go in another room such as the kitchen? She doesn't give any warning where she's going to go or when. Any advice is welcome. Thank you!