When the waist band of pants or skirts rides low on the hips, it often exposes the waist band of the panties underneath. This is a good opportunity to show off one's choice in panties, pretending to be clueless and classless in the process. This can be particularly effective when she sits on a bar stool.
Go to the girls department of a clothing store and buy the silliest pre-teen panties with cartoon characters, rainbow unicorns, or glitter stars. Be sure to get a size large if possible. Using some scissors, carefully cut away the hemmed edge around each leg hole. This will let the fabric pull up into her ass crack and pussy crack a little more than normal. It will also allow the waist band to ride higher on her hips all around, increasing its visibility. Now you are ready to take your grown up girl to the bar and innocently show off her silly, little girl panties.
Another option is for her to wear yesterday's thong, but be sure it is turned inside out, and have her put her legs thru the wrong holes as she pulls it on. This will position the waist band running down between her legs, and the crotch gusset will be up on one of her hips, facing out. This will feel a little different compared to usual, and portray a particularly clueless and classless image. If a stranger at the bar notices it and tells her about it, she should act embarrassed and head off to the restroom to remove it. A few minutes later she should return with the thong in her back pocket, with only a small part of the strap hanging out to be seen. If the stranger is still nearby she should thank them, turn to the side and swing out her hip and butt, pointing to her bare hip showing how she solved that problem. The thong in her back pocket should be just visible peeking out. She should offer it as a souvenir or as a thank you for being so kind. If they take her up on the offer she can pull the thong out, give it a kiss, and stuff it into the stranger's pocket, deep into their pocket.