Is there any possibility that she could have seen Lovelady and Shelley still on the first floor when she re-entered the front door at 12:36?
No, because, according to her testimony, she never returned to the first floor.
She entered the building, and took the stairs in the south east corner. They only went to the 2nd floor, so she walked through the office space to the freight elevators in the back. When she got there she saw two men whom she believed to be law enforcement officers. They all went on the elevator, but it wouldn't work. So, Adams came off the elevator and took the stairs in the north west corner to the 4th floor.
In theory it could be that, instant of going up straight away, she first went down the stairs to the 1st floor, maybe to get to the other elevator, and then went back up the stairs again to the 4th floor, but if she did, there is no mention of it anywhere. It could however, at least in theory, explain the sighting of Shelley and Lovelady