I don't know how to say no ..

Well I'm soooo tired of being a taxi. I'm almost 38 weeks and I just want to stay home. My SIL doesn't understand that, she lives 45 minutes away from me and she doesn't know how to drive 😡 when she was pregnant not to long ago, she wouldn't go anywhere her last few weeks. And I've told her I'm not driving anymore and apparently she wants me picking her up, taking her everywhere. Like hello ask you're SO not me please! I've had really bad back pains ever since I was 14 weeks till now, and everyday headaches. 😖 which she is aware of, but I'm  not sure how to tell her that I can't be taking her everywhere she wants... Advice anyone?