Pain can off course always be dealt out in a uncountable number of ways on a level that fits the crime. So i am not going to focus so much just on what hurts.
If you play with orgasm control and she cums without permission.Turn the attention away from her pussy and to her ass. (or mouth if anal is a no-no.)
If she forgets to ask where you want to cum, have her lick it up from the floor.
If she is a exhibitionist, you can use public punishment online as a means to punish her. For example punish her on webcam, make her go online and ask a stranger to jerk of to her.
Also old school traditional punishment would be to send her out to gather twigs and branches that she knows she will be spanked with.
Also making her write a short essay on how sorry she is and what she will do to make it right again.
If she speaks out of line, you can make a slightly painful tongue gag out of pencils and rubber bands. Eventually work on her deepthroating skills
Also you could demand she be your footstool naked for maybe 20 minutes while you watch TV. Or the more classical corner time.
Send her to the store without panties and a butt plug in her ass.
Make her continuously trash talk herself for a couple of minutes and tell you all the naughty things she is and that she likes to do.
Shove her ass mouth and pussy full of icecubes and make her stay on all fours until they have all melted.
Put toothpaste on her nipples, ass and clit.
Make her drink as much water as she can and hear her beg to go to the bathroom after a while.
Drag her into the shower and give her a cold shower until she has learned her lesson.
Make her write degrading words on herself, or you can do it.
Messy punishments if she would be into that, food/spit/makeup smearing, goden shower, etc.
You could revoke her underwear and pants privileges for a day..
Making her act like a puppy/kitty for an hour and meow once for yes and two for no. Those knees will hurt pretty bad after awhile.
When it comes back to pain again, you can off course use:
a spatula, hairbrush, pins, something resembling a crop, uncomfortable bondage, a belt, candle wax and the list goes on forever.
There you have a bunch. Many is probably not for you guys but some of them has to hit the nail