。
She turned to that medicine as a last resort.
Literal
She [topic-は] last [genitive-の] means [as-として] that medicine [on-に] relied.
頼る ('to rely on, depend on, turn to') marks the thing relied upon with に: 友達に頼る (rely on a friend), 暴力に頼る (resort to violence), 薬に頼る (lean on medication). The framing 最後の手段として ('as a last resort') signals reluctance and constraint — she didn't want to take this route, but ran out of better options. Combined with 薬 ('medicine'), the sentence carries a hint of 'finally giving in to medication' — possibly painkillers, sleep aids, or anything used unwillingly. The neutral past ~った lands as a flat report; no judgment, just a fact.