We have a dog door, fenced yard, mine have always been independent and able to go out anytime to do their business. About 6 weeks ago Topper started refusing to go out, I only realized it when he soiled the house for the first time in over 10 years. (He will be 13 Oct.1) I realized that the other 2 were going in and out, but Topper wasn't. I started taking him out briefly just in the front yard or across the street morning and at night, and my husband took him out a couple of times during the day. He loves to walk in the neighborhood, but at night or dark-morning, he only wanted to just do his business and run right home. I have no idea what caused his change in behavior, I was very happy to see him going out the dog door this very afternoon!
Something may have frightened Zaire while she was out at night, if so you will have to use a lot of positive reinforcement and hopefully, like Topper, she will start to feel safe again out there.
Motion lights may help, I have devices called "Pup-lights" that are like the human 'headlights' but they hang under the collar and light the way for the dog, designed for those who run or bike with dogs after dark. We use ours mainly at the dog park and Eddie loves it, runs like a maniac with all the other dogs following him and his 'headlight'.
I'd bet something spooked her and now she needs a change, walks out front for awhile, then you going out with her in the yard on a leash and learning she is safe there at night.
Good luck!
Anne in Tampa