。
She's working hard to become a model.
Literal
[topic-は] model [into-に] become effort [object-を] is-doing.
努力する ('to put in effort, work hard') is the standard verb for sustained striving toward a goal. The construction Xになる努力をする ('make the effort to become X') stacks a purpose clause inside the noun 努力 — 'an effort to become X,' which gets done with をする. The ~ている form makes this an ongoing endeavor. モデル is a loanword referring to fashion/photo modeling.