Carolyn,
Personally, I would rule out any problems with your Rat Terrier being spayed in the past. It's been too long and not the type of problem she'd develop.
From what you say, she might be having submission issues, where she feels the need to openly abase herself or hide for safety. Do you have any young children or other individuals in the house who try to drag or push her around? Does anyone yell at her? Don't mean to be rude, but one of my dogs showed a similar behavior when a former spouse was cruel to her outside of my presence.
Perhaps you would consider taking her to a veterinarian to have any health issues ruled out?
Also, take a look around at your household patterns. Is it really noisy, a lot of yelling, stressful, chaotic? There is a fight or flight instinct in dogs, just like any animal. Her instinct might be to hide from what's bothering her. She could also have developed a sensitivity over the months and just doesn't like it anymore.
If she's doing the rolling over and peeing when you bend down to pet or touch her, change the situation. If she rolls over...just ignore her and walk away. Have her come up to you instead. Just be gentle and quiet to build her confidence up. Since you didn't go into too much detail, that's all I can guess about what is going on.
good luck,
toodles