Actually, she is a mistress, specifically, her sister

Ava nervously looked at the bed, and when the person on it sat down, her heart sank. She was her older sister, who was in her second year of college at 20, and they didn't get along very well. Her sister, Jane, had always hated her, albeit always with her back to her parents. When she went to college she had barely maintained contact with her, and when she visited, she tried to be as far away from her, although she swallowed her hatred when her parents were around. Ava she thought like crazy, trying to figure out why the hell her sister would have agreed to be her lover.

Jane stood up, stretching, clad only in a thong, exposing her C-cup breasts, in contrast to her little sister's B-cup breasts. Her hair was long to the middle of her back, curly and brown in color, while Ava was a redhead, with a pixie-style hairstyle and freckles running down her cheeks. Jane had always been jealous that her sister was prettier than her, despite having smaller tits. Her innocent style and her blue eyes captivated anyone, something her older sister always hated.

Yawning, she walked past Ava's 'bed', giving her a single look, still tired, before going to the bathroom. Ava gulped, trying to reduce what her mouth was steadily producing thanks to her gag, listening to the shower jet open.

The sound of the water falling was like ****, as her bladder reacted and called more urgently for a release. Her pussy let more liquid flow, staining her bed, in fact, she was totally wet in the area where she would have rested her vagina. Although the night before she had fallen asleep in her own bed, in this universe it had been here, so she deduced that her pussy would have been expelling liquids all night, especially if it was connected to her need to urinate and she had to do it once every two hours.

As time passed, the more nervous she became, begging her sister to finish and allow her to urinate. It is true that she would be ashamed if she had to do it through giving her an orgasm, but she preferred that to being all day wanting to piss, even less if her desire would increase. After almost half an hour, in which Ava had clenched her thighs together, put her hands on her pussy tightly and was moving from side to side, Jane got out of the shower, a towel wrapped around her body and drying her hair.

"What's up, bitch?" Jane said with a smile, laying the towel on the bed and letting her wet hair fall down her back.

Ava frowned and tried to protest the insult, but only grunts came through the gag. Jane just laughed heartily as she opened her closet and pulled out some clothes.

"I know you don't like me calling you that, but in case you don't remember, our parents were delighted that I was your mistress and officially expelled you from the family. So I can call you whatever I want" she said as she looked at Ava with a mocking smile.

Ava moaned desperately, not wanting to believe what she was hearing, her parents couldn't be that cruel. But everything pointed to that Jane was telling the truth, in this reality, her parents preferred to leave her in the care of her sister to haven't to take care of her more. She started crying openly, but Jane completely ignored her as she undressed and dressed in whatever she had chosen. Ava was heartbroken, until recently, she was a normal girl, and now she ... she had been sent to a universe where she was nothing more than a ****.