thank you for sharing Rebecca horny moments! The Photos and videos you've recorded are simply awesome.
You're asking how to push her limits.
If I was her bull, I would ask you to prepare Rebecca binding her wrist and legs to the bed with ropes. After, to lick her pussy until it gets wet and she's begging for being fucked.
I agree with other bulls, it's great to fix the leash of her collar to the bed frame and fuck from behind....
there are further subtle games that can be made starting from there
Please let us know more and watch some other photos.