You get it in the end.

"Glad you are ready, but you need to get me wet first. I'm gonna have to train you on the order of these things. Lube first, then anal." She smacks your ass until you understand.
You turn and see the dildo is right at your mouth, so you lick it all over to get it wet, then spit a gob on the end.
"Good?"
"Very much. My ladycock thanks you."
She then helps herself by spreading your cheeks and guiding her rubber cock into you. It is not as large as you had hoped, but good enough.
"Wowzers! I slid right in!"
"I'm just that good," you proudly state.
"You sure are! Wow, way to emasculate my cock fantasy! I was hoping to really have to work it in."
"Well make a bigger one," you tell her.
"Well I'm gonna make use of this one first!"
She starts pounding your ass hard. You are pulled and pushed as you lay over the couch. You actually get rug burns on your chest before you decide to lift up. You turn to see her ramming into your butt full-**** with her eyes closed. Her boobs jump around as she goes at it with your butt. She occasionally smacks your cheeks too.
"What are you thinking about?"
"What it would be like if I had a real cock fucking you," she answers after a pause.
"After that demon encounter, a real cock would be too small. You need an unreal monster cock."
"With a big fat bulbous head to get stuck in you like you prefer. Oh yeah," she shudders, then falls forward on your back for a moment before regaining her composure. "That was good, thanks honeybuns. Do you want me to keep going?"
"No, I've cum as much as I can, I probably couldn't again."
When she stands, you notice her bulge is larger. She doesn't notice so you point it out. She does the same to yours.
"Shouldn't they be getting smaller as our bodies absorb the cum?" you ask.
"Well, it's shemale demon cum, not normal cum. It must not work the same way."
"Yeah," you dismiss it. "I better put my underwear on before I make more of a mess."
"Yeah, me too," Amy says. When she spots the mess, she says wistfully, "I should make you lick it up."
"Hmm, oh right, my clothes were destroyed."
"Oh, um...wow your butt wouldn't fit in them anyways...I was too rough, wasn't I? Uhm...you can borrow one of my thongs."
"Oops, forgot I still had this on," she says holding the strapon.
"Why not leave it on?"
"Don't be silly..." she says thoughtfully.
"It suits you."
"Why is your chest all pink and swollen?"
"You gave me rug burn," you frown.
"Just be glad you don't have these puppies, or you would really be hurting." She grabs her breasts firmly.
Amy wanders off to fetch some clothes. You look down. Your nipples are especially bad. They are swollen to three times their size.
When she returns, she is wearing a bikini top with the triangles perched on her nipples and leaving the rest of her breasts bare. Below is a thong with the front bit of cloth stretched to lewdly perch on the end of her dildo, and a mostly see-through sarong around her waist.
"Here is yours."
"Thanks, you look good," you tell her as you take the red ball of string, not remembering when you agreed to wear this. After you slip it on, you see it does fit properly...at least more properly than Amy's current bottoms.
"You will need more than a thong," Amy tells you.
"All I have is a thong," you remind her.
"Well, not like our old stuff would fit anymore with our bloated bottoms. You will have to wait here while I go shopping." She grabs her keys and her credit card and goes out the door, just like that.