I wonder why she would need what appears to be a whistle? Unless she has an animal companion she calls to aid her?

It could be a dog whistle or a signaling device to make contact with her fellow rangers. Hiding messages among the background noise of the forest seems like something they would do.

AdventZero said:

It could be a dog whistle or a signaling device to make contact with her fellow rangers. Hiding messages among the background noise of the forest seems like something they would do.

It could also just be a duck call to hunt with.