Dog won't go down stairs. Need help quick!

We adopted a dog last night. She went up and down our stairs a few times until one time she slipped, we have wood floors. The next two times we tried to coax her into coming down she pee'd. I quickly ran to home depot and bought drawer liners to put on the steps and now there is good grip, but she still won't go near the steps. Treats are not effective. She is 50lbs coonhound. She has not poo'd yet today so we really need to get her outside. She can't stay upstairs forever. What do we do!?