Sister taking advantage of me...

I’ve always been a homebody and I prefer to be home in the comfort of my bed with a book. My older sister on the other hand, likes to party, socialize and go out otherwise she starts to feel caved in. We’re complete opposites but it works, she tells me her crazy going out story and I try to calm her down during hangovers. She has 2 kids and I have 1 and currently pregnant with baby #2. I’ve been temporarily living at my moms for a year until my house is complete being built, and will be moving out in a week. Thank goodness because for the past year; my sister has used my company to watch her kids while she goes out. After a while, and being exhausted (both she and I work) I started to refuse watching the kids when I knew my body and mind couldn’t take it, she would then lie about it, like today. Our kids go to the same day care so I drop them off and pick them up. She went out and told me specifically that she’d be back by 4pm, and it is now nearly 8pm and she’s still posting pictures that she’s out. She’s done it again.. withhold information so I have no choice but to watch her kids. I’m so fed up and I’m so ready to move and cut her off and not have to be put in this position. I love her and my niece/nephews but having to watch her kids 3-4x week in addition to watching mine and being pregnant is tough, I need a break too. But the worst part is, she makes fun of me for saying I don’t have friends and i’m a grandma that doesn’t know how to have fun. 🙄