Easiest thing to do is, stop depending on your sister for honesty. If she says the event starts at 10, check independently, and then show her. "No, ___, it starts at 9, see?" She will undoubtedly claim she was mistaken, or it's a misprint, or she was confused, or she was joking, or whatever and will deflect til the cows come home.
Do it again and again. You'll save your sanity by really knowing when things start, etc., and you'll be telling her that you're onto her. You know she's unreliable. Her daughter won't be left homeless.
Also, in all seriousness, habitual lying could be coming from some sort of underlying illness. She has nothing to gain by telling you that the movie starts at 10 instead of 9. It might be a good idea for her to get a full medical checkup.