maymie, your feelings are valid and certainly understandable so please don't beat yourself up!
I agree that being direct with her may be your best option...don't assume that she truly knows that you want this time alone with her.

I'd like to add a personal experience, and I offer my apology in advance if you are offended...
During the Vietnam war, I served two tours as an Army nurse. In no way can I adequately express the bond that develops between people serving together during war time. #1 is a quiet slip into trusting another person to cover your back while you are also earning their trust.
There is never any intent on leaving any family or friends out of your life, nor is there any desire to hurt them. Quite frankly, we need reminded there is life after combat situations.
Please give your sister that gentle reminder and she will respond to it. It did take me a few months when I came home to remember what it was like to be a civilian...
To this day, there are "buds" that I would take a bullet for and I know they would do the same for me.

Her action is no reflection on you...it's more likely a reaction to being home and wanting all your loved ones together.
Transition to civilian life is hard on everyone.

Best wishes!
Cap