Well, trying to do it with burns certainly isn't the easiest way of doing it. For one thing, the tool is gonna lose heat pretty fast, and it's not going to burn evenly.
When it scars it might look good, for a while, but as it slowly heals (assuming she doesn't go for skin grafts or the like, which I think she might avoid unless she can find someone she's sure won't talk) the words are gonna blur and distort until its just a mess.
So, the simpler the better, basically. Initials are best, symbols better still, but trying to write "Anon wuz 'ere" on her ass and thigh with a screwdriver you've run through an induction furnace is just gonna be more trouble than its worth.