Why does she keep weeing inside??

[Trina]

I have an 8 year old (approximately) unspayed female Basenji. I have had her for nearly 3 years and got her from a registered breeder who bred a few litters of pups from her.
I understand the nature of the breed very well and I have had one before that I had since a pup. As is usual Basenji behaviour she hates going outside to the toilet when it is wet or cold and hates walking on grass. I have a cat/dog door and she is free to come and go from the house at all times. It is a constant battle to stop her peeing inside in the winter but it is now summer here and she loves going outside and has been pretty good at going outside to toilet…... until yesterday.

First thing in the morning when I get up I encourage the dogs (the other is a Jack Russell) to come outside to go wee, even though they can go out the cat door. I left the door ajar as I went out and they followed, as I was watching the JR I didn't see that the Basenji has gone straight back inside and promptly did a huge wee on the kitchen floor! It was not cold and it was not raining. I caught her just finishing and scolded her and locked her outside where both the dogs stayed while I was at work. They normally would have access to the house when I'm at work.
When I got home there was the usual happy greetings from both and I decided they could be let back inside............when while I was bringing groceries in from the car she did an even bigger wee inside on the kitchen floor and half on her bedding!! I was furious and she knew why as I caught her as she was finishing again and I locked her back out.

It looked as if she had saved it up all day, there was that much. So for the first time since I've had her she is banished to outside for the night. I have put a coat on her and she has a cosy bed but she is very unhappy about this. Please help. Why is she doing this?? What can I do?