Hissing Dwarf

[Mawuu]

Hello I'm new to owning hamsters, I just received my girl yesterday. Her name is Luna she's a 3 month old winter white dwarf.

Today I wanted to fix her bottle and add a new toy. She lives in a stack 2 bin cage her bottle being on the top floor and the toy I added today being on the bottom floor.
Things where okay at first, I couldn't tell which floor she was on since she was hidden. So I did a light pat down of the bedding to smooth it out after I fixed her bottle. I then had picked up her top floor and handed it to my brother so I could add the toy to the bottom floor. At this time I wasn't looking at my brother but she started to hiss as he had accidentally found her with his finger. I finished quickly and put her cages back together and she's been hiding since.

I believe my biggest mistake was bothering her so soon and doing so when she was hidden. My brother did not wash his hands either and I didn't know he'd stick his finger around in the bin (he's older then me and we are both adults).
I feel terrible I really don't want her to think Im a threat or make her hiss again its sad to know she was so scared. What should I do to make her comfortable?