I'm not sure what she meant by "disguise is self-portrait"

Native speaker’s answer
Rebecca
"Disguise is a self-portrait" means that one's disguise often ironically involves being themselves in some form instead of being a completely different person. Perhaps because they get to act more naturally, or because they get to portray parts of themselves they don't usually portray. Ex: I feel more myself when I'm acting on stage. The character feels like a self-portrait. Ex: I sometimes pretend I'm the characters in my book so that I can write easily.