In the X-Men, Rachel Summers had these branding tattoos on her face that she got when she was a slave. She typically covered them up by casting the psychic illusion of an unmarked face. Thing is, even when she was asleep or knocked out, her face remained unmarked. She held the illusion for so long, it was like a natural reflex.
Ditto with Cable using his TK to keep his techno-organic virus at bay
And Mystique half the time
Candice could've jumped back to that slim form if it's her natural default illusion.