I like to fuck her ass hole

vaseline

Female assholes are elastic , they expand.
She has to relax.
If she tenses up , it won't work because she will scream in pain.
Deep rim her poop chute and lube it up with your saliva and fingers.
There's nothing wrong with a little poop on your tongue and in your mouth when you deep rim her shit pipe.
Lube up your cock real good with K - Y Jelly so it slides in nice and easy.
But make her promise to blow your dirty cock when it comes out.
A woman's ass is not just an exit only.

Firstly, I agree with the above poster on the but plugs idea, and of course plenty of lube. Also, before you enter, play with her butt, finger her, maybe use your tongue if you like. rimjobs are a great way to help her to relax so her ass will expand, plus they can be pleasurable for her.

If your not into rimming, just use your fingers until she is relaxed.

Try Astrogel lube the crap outta that.
At least she allows it most chicks avoid it like a plague.

You need to get some smooth jizz stuff. No one would enjoy a hard dry cock up their arse. there are loads of these on the market. Just google ann summers. If you get her to stroke it onto your cock you will get even harder and it will be better for both of you.

Buy her a butt plug, increase the size every once in a while until she gets the right size.

If big thick 6 - 8 inch logs can come out of it , then a 6 - 8 inch long thick cock can fit in it.
A woman's asshole is elastic , it expands.
Tell her to relax because if she tenses up , then it will hurt and it wont work.

Loosen it up with K - Y Jelly and your fingers at first.
But make sure she sucks your dirty cock when it comes out of her poop chute { shit pipe }.