After typing your girlfriends request, the transformation began.
She grew taller and fatter, her belly sagging to below her knees. Once her head reached the ceiling, the room began change too. It grew with your girlfriend, adjusting it's height and width until she was 50 feet tall and weighted 30 tons. Exiting the room, to make sure the building wasn't going to collapse, you discover that the room outside was the same. You came to the conclusion that your room only grew bigger on the inside.
As you re-entered the room, your giant fat ass of a girlfriend started turning purple. Her belly was a light purple while her pack was violet. Her body developed scales and a tail had popped out of her back. Her hand and feet became clawed and two horns grew out of the back of her head. Her face had become draconic in appearance and her ears looked like they belong on a hippo. Her wings stretched from her back, their intimidating size and shape sends chills down your spine.
The transformation ends, and your dragoness girlfriend looks down at you with her beautiful purple eyes. She moans as she rubs her tummy, ecstatic in the rumbles and groans it made. A thick light green gas escapes her rear, making her moan louder as she smells it.
She smiles, as if she just gone done sudducing you.
You admitted to your self that if that was the case, then it worked.