You decide the easiest way will be to simply nab the amulet from her bedroom, but also the most dangerous one: from your infrequent visits to the guest room, you happen to know it has a creaking wooden board floor. If you'd try to sneak in right away, the guest would probably wake up and notice by the noise. You need to make yourself stealthier, and especially lighter as to prevent the boards creaking under your weight...a rat would probably be of suitable weight. That's it, you can use your adoptive mother's magic potions to change yourself! While she's in the garden, you decide to sneak into her study chamber and you take a look at the transformation potions. "Cat...horse...rabbit...ah! Rat!", you think as you grab the bottle off the shelf and quickly make your escape. You hide the bottle in your room, and wait until nightfall. Once you've stepped into your nightgown and got your night kiss from mother, you get out of bed and take out the bottle. "It's this or nothing", you think as you swig the potion down.
The moment you drink it, a coat of fine white fur starts to sprout all over your skin. Your hands and feet turn long and clawed, and your face is pushing out into a round muzzle with whiskers. Molars recede, and your two front teeth grow to enormous buck teeth that almost fill your mouth. Your ears become rounder, sliding into furry dishes on top of your head. Your eyes turn from their normal color to white to ruby red, marking the completed transformation of your face. You feel your spine stretching, and within moments you can see a long, pink, hairless tail squirming from beneath your nightgown. Now the final phase of the transformation commences as the gown's fit becomes wider and wider, until it drops off you and you end up being barely a foot large. You took care to leave the door open beforehand, making your exit from this room a lot easier. Scurrying across the hallway boards on your rat paws, you finally come to the guest room door and it seems this lady has the same habits as you regarding doors. You sneak in, and with a quick scaling of her night table you grab the amulet between your teeth. You are a bit slowed down because carrying the amulet like this is difficult, but you manage to make your way back to your room. Now, the question is what to do with this thing...