Do you have to bring her with you? Can you get a cat sitter and leave her at home? It is really torture to make poor kitty stay in a carrier sitting in her own filth for 24 hours.

If you can't leave her at home and have someone come in and feed her, give her water, and play with her, you may consider trying to leash-train her before you leave. That way she isn't stuck in the cat carrier for 24 hours. Ask your vet about drugs you could give her to relax her.