。
She is self-conscious about her looks.
Literal
She [topic-は] her own appearance [object-を] is-worrying-about.
気にする ('to mind, worry about, fret over, be self-conscious about') is the standard idiom for fixating mentally on something. The progressive ~ている marks an ongoing state of mind rather than a one-time worry. Note that 気にする pairs naturally with concerns one wishes to but cannot let go of — distinct from 気をつける ('to be careful, watch out for'), which marks active vigilance.