。
When she finished her coffee, she ordered another cup.
Literal
She [topic-は] coffee [object-を] finish-drinking [when-と] another cup ordered.
Two interesting verbs. 飲み終える is a compound verb formed from the masu-stem 飲み + 終える ('finish'), giving 'finish drinking.' Compound verbs like this are everywhere in Japanese and let speakers tack a result-flavor verb onto an action — 食べ終える, 読み終わる, 言い切る, etc. The conditional ~と here means 'when, as soon as' — it links two events in sequence with the implication that the second naturally and immediately follows the first. もう一杯 uses the counter 杯 (for cup-like drinks), with もう meaning 'another, additional.'