。
She made sure he couldn't see her tears.
Literal
She [topic-は] him [by-に] tears [object-を] not-be-seen [in-order-not-to-ように] did.
A bare-bones version of the ~ないようにする pattern: 'make sure not to, take care that X doesn't happen.' Without an explicit follow-up clause (like a 顔をそむけた), the matrix verb is just した — 'did so as to (prevent X).' This frames the whole sentence as a deliberate effort, with the specific means left unspecified.