。
She makes a living as a writer.
Literal
She [topic-は] writer [as-として] livelihood [object-を] is-establishing.
~として ('as / in the capacity of') marks the role someone occupies — 教師として, 友達として, 親として. It doesn't merely describe; it foregrounds the relevant role in the action. 生計を立てる is the set phrase for 'make a living,' literally 'to stand up one's livelihood' — 立てる ('cause to stand') here means 'establish, set up.' The progressive ている marks an ongoing state: she's living this way, not just doing it once. 作家 ('writer, novelist') refers specifically to a literary author, distinct from 著者 ('writer of a particular book') or ライター (loanword 'writer,' often for journalism/copywriting).