You rush into the first door on the right, slamming the door behind you.
The room you find yourself in is light by a single bulb hanging from a cord connected to the ceiling. It sways back and forth from the wind of your abrupt closing of the door. It's cream-colored walls are un-decorated save for a few hooks on the far wall and it's only furnishings are two white, wooden benches with green and white cushions on the seats placed at opposite ends of the room from each other. Perhaps this was some sort of changing room? You search around for a hiding place, but you clearly chose the wrong room for that, as you can find nowhere you could hide where you wouldn't be spotted immediately.
Your heart tightens in your chest as you hear the door fly open. You shriek and spin around instinctively to find yourself face-to-face with the angry woman from before. She wears a plush, blue bathrobe with matching slippers. Her shoulder-length wavy ginger hair is free from adornments and a few stray locks hang over her pale green eyes. She pants from the frantic effort of chasing after you, her back hunched as she keeps her left hand slayed against the door you just walked in from.
"You...are no mistress of stealth, young lady." she says through her panting.
"I'm sorry." you say, backing away from the woman.
"You must have seen the sign. 'No tresspassing', sound familiar?" she asks as she catches her breath and stands up straight, folding her arms in front of her chest as she lifts her chin indignantly.
"I'm sorry," you say "I'll leave, I'm sorry." you stammer, your own breathing getting heavy from the panic of having been caught not only trespassing, but entering and stripping in a strange house. It occurs only just occurs to you that you've been doing quite a few strange things today.
"No." she says and uncrosses her hands. She cups them both slightly and moves her right hand over the left as though she were holding an invisible ball. She inhales and narrows her eyes, which glow slightly as a flash of light appears in her hands before instantly disappearing and being replaced with a dog collar. You scream again at the sight and press your back against the far wall, your breast heaving with fear. Her scowl turns into a wicked smile as she pushes her hands out towards you. The collar flies towards you and snaps firmly around your neck.
"No!" You scream and pull at the collar, but no amount of fumbling with the band around your neck allows you to find its clasp.
"If I let you leave then you'd be a trespasser, and we can't have that. No you'll just have to live here now." she say and steps further inside the room, closing the door gently behind her. You're fingers seem to be getting numb and clumsy. As they rub together in your attempts to free yourself of the collar, you can't help but notice the feeling of hair. You pull your hands away to see that fur has coated your hands, and your fingers are shortening as they change into the paws of some sort of dog. You scream again and try to move them back to your neck, but your muscles change as the fur crawls over your wrists and down to your elbows. You can feel fur pushing under the collar and sliding up your neck and down to the small of your back. You try to beg for mercy but your mouth pushes into a muzzle and your teeth and tongue begin changing into a canine form, so all you can form are grunts and whines. You feel two pointed ears grow from the top of your head as your old human ones disappear.
"Fortunately enough for you, my new pet, I happen to need a guard dog. Now..." she says, with another flash of her hands a leash appears and flies forward clipping itself to the collar around your neck. She gives a slight tug and you find yourself falling forward. As your paws hit the ground, you feel your back shift, and your legs...your back legs, shorten. The fur continues marching down your sides as your breasts slowly fade away into nothing. Your back legs, now fully canine, are quickly coated with fur. The last bit of change comes when your tailbone extends into a bushy canine tail, which tucks under your legs in fear as you whine before the human which now towers above you.
"Now now, don't be frightened." she says and kneels close to clutch your face in her hands "You're my pet now. I'll take good care of you." she says in a comforting tone. You try to hold on to your fear of your mistress, but she seems so much more wonderful now that you can't seem to keep your tail from wagging in her presence. After she begins scratching you behind your ears you slowly stop trying to fight it and accept her. You find yourself panting happily and licking her a few times on the face, causing her to laugh.
"Good girl. Now come," she says and stands, giving your leash a bit of a tug "I need to take my bath. I know you'll keep any more trespassers from entering our home." she says and begins leading you out of the room before turning back to you "Unless you want a friend." she says with a wink. With that you follow your mistress out of the room, your old life having faded from memory.