This is the 7292nd most frequent Russian word.
выбирая
"Choosing" or "selecting."
The word 'выбирая' here is a present participle meaning 'choosing', showing the action of choosing clothes during this process.
Выбирая одежду, он всегда учитывает погоду.
Choosing clothes, he always considers the weather.
In this case, 'выбирая' emphasizes the action of selecting among options while she stood.
Она долго стояла у полки, выбирая книгу.
She stood for a long time by the shelf, choosing a book.
Here, 'выбирая' signifies the process of making a choice during the act of decision-making.