I too really enjoy having my characters end up in bad situations; I just like the role-playing aspect of these. Often times, I try to set the situation up at the start of play, but few of the people I play with (even DMs/GMs) have really been able to run with it. A few examples...
1.) In L5R, I played a dishonored samurai-tactician. He had recently thrown a battle to protect his beloved. No one knew that he threw the battle, and he was simply believed to be incompetent (not a traitorous dog). He had to shave his head and join the monastary. He continued to adventure with his old group, now as a monk rather than a samurai. He was constantly tormented by his former beloved, a Matsu berserker (and fellow PC), who had no use for some one no longer from her own caste.
2.) Also in L5R, I played an amputee shugenja who had been ransomed to another of the Great Clans, one who really hated her clan. The other party members semi-abused her (I thought they should have been more abusive), but could not ouright kill her because one of their beloved family members had been co-ransomed.
3.) In D&D, I have played a wizard who was caught cheating at her classes and appropriately punished: stripped of her ability to cast arcane magic and transformed into what the school called a drudgethrall, a deformed little creature (equal parts igor and quasimodo). I actualy advanced the character as a rogue (not wizard).
4.) Also in D&D, I have played a rogue from a small guild-town who travelled to a larger city on some guidl business. While there, she was captured and ultimately indentured to the care of the party. Chiefly, she was supposed to act as a guide through the wilderness near the town from which she originally hailed.
5.) Finally in D&D, I have played an elven binder/wizard who was a student at an adventurer's academy. When it was discovered that she was researching illegal magics (i.e. binding) she was stripped of her "student" status and made a henchman for her former friends. She got payed a henchman's salary rather than getting a fair cut of treasure (in all fairness she did get a normal cut of magical treasure, the group realizing that she was teh only one amongst them who could use certain items), work at any banquets in the group's honor, and do odd jobs around the school. Her sister, an elven fighter (and co-player) tormented her somewhat, constantly threatening to tell their parents about the characters loss of status at the school.
So, suggestions for tormenting your player:
1.) loss of social status, especially in a way that makes her subservient to the rest of the party
2.) maim her, amputate a hand, an ear (or part of an ear), a finger, or some toes; maybe make her completely deformed (a hunchback and clubfoot comes with some DEX, CHA, and speed penalties)
Find out in advance maybe if she is fine with some of these ideas, be they temporary or permanent, as they are not quite as "cool" as becoming a bloodthirsty demon, and may be different than what she is looking for.
Chad