Note: It said that you need to drink a whole vial for full effect, so there's no leftover. So I'll assume she put the empty vial back to get another one.
Her belly got rounder and rounder. She felt a pressure from inside, and a strange sort of expansion. It was like there was a watermelon inside her. She also felt sick. Then something kicked inside her swollen stomach. She knew, then, that she was pregnant. But how could that be possible?
Yet she also knew that if turning into a cow was possible, surely becoming pregnant wasn't any less possible. And she had a pretty good idea of how it happened.
Because she's female, and she can't get any more female. If she drinks another female vial, and she can't become more female, it would have to make another female! She knew, then, that the child had to be a girl.
Mary began to feel pains, and barely made it over to the bathroom, but since she was getting pregnant really fast, the pains were going and coming really fast, too. She didn't know what to do--if she called a doctor, at the rate she was going it'd be over by the time she could reach the doctor. Finally she tried to lie down in the tub.
The pains continued, and she felt herself having to push--but constantly, over and over again. Her pregnancy had developed so fast that she pushed the baby out in a few impossible seconds, and then the afterbirth came out immediately. But at this point things had slowed down. The cord fell off as the baby aged to one month old, but at that point, everything stopped.
And as she had guessed, the baby was a girl. It had her eyes and nose--in fact, it looked just about what she must have looked like as a baby.
Mary felt a bit of bloating in her chest, and realized what she needed to do. After cleaning everything away, she picked up the baby and let it suck from her breast the nourishment it needed.
Mary knew that magically having a baby from nowhere could cause problems. First, nobody would believe it's hers unless she showed them the vials. Second, she couldn't take care of a baby and work. So this couldn't go on forever. But what could she do?