Make up an excuse for you being there.

“Hey sis” She covers her breasts after she hears you. You cant really see her clearly through the shower door and if you want to see her in all her glory you need to look inside.

“Why are you in here?!” She says

“ I need to get my razor it’s in the shower” you answer. Maybe this will make you see her naked

“Why couldn’t you just wait im in the shower.”

“I really need it now I have to go soon”

“Fine one sec” she says than goes to grab your electric razor.

“Here.” She open the glass door extending her arm outside handing you the razor.