She use to go up and down the stairs of our deck all by herself to go potty. And now she absolutely will not do it! She will go up and down the stairs inside our house, but not the deck. I thought maybe because she's too cold or something to go up the deck but today, the weather is wonderful. She's been outside (in the shades) for awhile now and will not come upstairs. She'd go like half way or even 1-2 steps away from getting on the deck, but then she'd stay where she was. Or when I check on her, she'd run all the way back down stairs. WHAT IS THE DEAL?