。
She woke up on her own.
Literal
She [topic-は] of-her-own-accord eyes [object-を] woke.
ひとりでに and ひとりで look almost identical but mean opposite things to a learner: ひとりで is 'alone, by oneself' (the agent does it solo), while ひとりでに is 'of its own accord, by itself, automatically' (no agent involved at all). Here ひとりでに says nothing happened from outside — no alarm, no parent shaking her shoulder — she just woke. 目を覚ます ('to wake up') is a transitive idiom literally 'to make one's eyes wake' — distinct from 目が覚める ('one's eyes wake up'), the intransitive partner. The choice of transitive 覚ます subtly emphasizes that the waking was an act, even when self-caused.