Boundaries and family

Hello –
I am trying to understand boundaries with my family. My sister and her husband are not people that I would be friends with. They are family. I lover her for who she is. But when we get together she’s so negative. I am at the point in my life that I don’t want to be around negative people. Instead of just pushing her away, can I have conversation/set a boundary that when she enters my house she needs to be postive? If not, please don’t enter? I feel that I’m trying to control and ask her to be someone she is not. I want to say that if you’re going to be negative toward me in a conversation – I will ask you once to stop and then I will end the conversation. Does that make sense from a boundary standpoint? or am I totally missing it? Thank you!