As Mary Lynn pulls you in towards her, with her fist wrapped around your torso, you know you have to act fast. You pull your left arm, still holding the gun, as hard as you can and free it from her first. You turn the setting to "shrink" and point it at the giantess Mary Lynn. "Take this, bitch!" you shout, and you fire.
Nothing happens. Mary Lynn unfolds her fist as you stand on your palm. She's still a giantess compared to you, though she seems confused herself, and more so than if nothing had happened. She's already looking around in shock, and when you do the same, you make a startling discovery: you've both been shrunk!
You're both still in an otherwise ordinary row of books in the college library. But Mary Lynn is not even tall enough to reach the first level of books, and you're so small you're standing in the palm of her right hand. You shudder to think of what your height must be now. A fiftieth of an inch? A hundredth? You need to resolve this, and fast.
Especially since you glance to your left and see Mary Lynn's titanic left hand coming at you. More specifically, she's leading with her thumb and index finger closely together, as if she wants to pluck you, or something away from you. That's when you realize she wants the gun: she's realized that if she can pry the gun away from you, the gun will change its size to fit her. You can't let that happen, so you wrap your arms around the gun. "I'll destroy this thing, I swear!" you say, but it's an empty threat and you know it. And apparently, so does Mary Lynn. "Oh really?" she asks. "I'm sure you'd like it if I put you on the ground and just left you here. How long do you think you'd survive? You're not even a fraction of an inch tall."
She's got you on that one, but still, your mind is racing. You realize your problem: since you were touching Mary Lynn when you fired the shrink ray at her, you were shrunken too. Makes sense. Your next move, though, requires a neat trick, since you're still standing on the palm of what looks to you every bit a giantess. You surreptitiously switch the gun setting to "grow" while Mary Lynn is still hesitating. Then, without warning, you jump in the air and fire at yourself.
Your plan works like a charm. You grow yourself back to your normal size, and Mary Lynn's still tiny. In fact, once you land on the ground, a normal person once again, it takes you so long to find Mary Lynn that you wonder if you'd accidentally stepped on her. But soon enough you see her, running away, and it's only a few quick steps before you come upon her and pluck her up with your fingers.
It's odd to hold someone that small in your hand. Usually anything that small and living is so filled with vermin you need to take a shower afterwards. But Mary Lynn is different, and you love feeling her squirm. You have half a mind to keep her like this, and find some way to torment her. Of course, she's been pretty dangerous too. Maybe you should grow her back and let her go back to her own life and hope you never run into her again.