。
Which one do you think she chose?
Literal
She [topic-は] which [object-を] chose [quotative-と] think [question-か]?
Wh-questions inside と思う move to the front of the sentence, ahead of 思う — so どちら fronts before the と marker, even though English keeps 'do you think' at the front. This 'what do you think...' frame is one of the most common ways to softly probe an opinion. Picking どちら over どっち shifts the register up — どちら is the formal cousin used in service contexts and polite speech.