Submissive urination

I have a small Female Beagle-Jack Russel mix. She is almost a year old, and used to be housebroken. For the past month, 5 minutes after she comes inside, she urinates or defecates. Doesnt matter how long I leave her outside, she always holds it until she comes back in. Also, everytime I open the back door to tell her to go potty, she rolls on her back, and starts peeing. I'm at my wits end right now.
Any help?

Why not take her out for a walk instead? Maybe she just feels very insecure outside by herself.