You sound like a fun group. Before the game starts, have everyone write one or two punishments and put them in a jar. In addition to being naked for the remainder of the game, the loser will have to draw a punishment from the jar and do what it says. That way, they won't get crazy because you might end up drawing your own punishment and you can also include spanking as one of them. She could just draw again if she chooses it.
Some ideas for punishments include:
1. Getting dressed again and performing a full striptease with music for the entire group. The dance must include two minutes fully naked! It is a little more embarrassing to have to dance naked for a group instead of just take your clothes off in front of them.
2. Perform the song, "I'm a little teapot" complete with arm movements.
3. Tell the group the last time you had sex with your partner and the last time you had an orgasm. See if the dates match or if someone has been having some solo time.
4. The loser has to be the waiter/waitress for the rest of the night serving drinks and snacks to everyone. They must remain naked while serving.
5. The loser has to have their picture taken with a bag over their head. You could write the date on the photo and keep a record of who lost each time.
6. Drink a shot of tequila and tabasco sauce mixed together.
7. Have people bring over their clothes that need to be ironed and the loser has to iron everyone else's clothes while being naked. You might allow just their underwear in case the iron is hot. People shouldn't bring too many because they might end up ironing their own clothes and then more.
8. For the next game, order pizza or other takeout food to be delivered. The loser has to answer the door naked or in their underwear so the driver can see. If they can get five dollars off, then they get extra clothes for the game that night. naked. It is really embarrassing for the guys!
9. The loser has to go one full day, to work, to school, to the grocery store, around the house, etc, without their underwear. This must be verified by their partner.