Perhaps have her chair changed to a kneeling chair to more show her position. Pictures can be seen on
http://www.healthyback.com/store/sit...elingchair.htm
As an added idea, this also changes access to the female anatomy while seated.

Have the underwear that shows up one day be a butt-plug harness, a chastity belt, or other pervertable.

Have her given a comfortable bra. Then called into the office first thing in the morning, have her bra replaced by ropes, and kept like that in breast bondage for the rest of the day.

She is forced to take off her shirt in the morning in the office. Someone writes something on her back in marker, and the shirt goes back on before a meeting. She doesn't know what it says, or if it's visible.

She breaks her leg. The signatures on the cast can be quite risque, and she can't take it off for 6 weeks. Visibility of the signatures all depends on length of the skirt allowed.