He becomes angry...

 The dragon shifted fully into its animalistic form.  He lunged forward and shoved her into the wall.  He fangs snapped inches from her neck, she could feel the change spilling through her insides, she could feel his semen swimming around in her bloodstream, and the beginings of children fertilizing in her womb.  She looked down to find scales growing like a rash from the ring about her nipples.  The dragon slapped her with one large paw and it roared at her.  "You dissssobeyed me!  How can I be your sssssex ssslave if you sssserve me not!?"
   In a deep snarl he tore his now giant cock into her.  As he fucked her against the wall his thick veiny slab of sexmeat grew, from a foot to two, the way he **** her there was no longer physically possible, his cock shoved deep into her body making room for itself.  Her lips dislocated as he **** her wildly.  She screamed and screamed out for mercy as he bit into her neck, sucking hard on the flesh of her.  As his monstrosity crammed inside her she could feel a tail sprouting, her tailbone elongating.
   The pleasure began to outweigh the pain and as he came wildly into her, jackhammering his hips into hers, she found herself screaming out in pleasure.  Now it was time to take control.  She pushes him onto the ground and sat on his cock, taking it throbbing inside her.  The angle was so tight that his prick could be seen pushing against her belly as she stood all the way up on tiptoes, so his handful of a sweaty head pressed to her cuntlips.  Precum practically shot like darts into her, each thick rope making a slapping sound as it entered her, like a normal erect penis would.  She, however, was so filled, that the sperm gushed out back down over him so that everytime she let herself fall from tiptoes down to his hips, his size pistoning into her, she landed in a puddle of cum.
   His tail writhed up, and the penile end pressed to her anus.  On her downthrust it slammed inside her, straight through the small intestine and back out.  She was screaming and screaming and screaming as he fucked her madly.  After fifteen minutes or so of this he threw her into the ground and grabbed her shoulders, sliding all his length into her, all two feet straight down to his base that had a five inch diameter.  His balls, each larger than his base, crashed into her ass leaving bruises.  The wet sounds were so loud they nearly hurt to hear, and her screams were almost drowned out, along with his feral snorts and screams as he blindly fucked his mistress.