Why do you have to supply the litter and food for someone else's cat you are watching, that is ridiculous and on that, I would have said no, regardless the amount of money being offered a definite NO! Don't worry she probably scammed another to do it for her, she isn't going to pay for a kennel if she is that cheap. My sister watched my cat when I went away for a week once when my roomie went away too, and I didn't even make her clean litters I bought a second litter box and filled both up, same as dry food and water in case she forgot to come in one day, cats will usually sleep if alone anyhow. I took my sister out to a nice restaurant when back home, that was all I offered for payment to her, she lived nearby and popping in once a day didn't put her out any, and I am sure she snooped plenty while in my place, lol.
“Accept — then act. Whatever the present moment contains, accept it as if you had chosen it. Always work with it, not against it. Make it your friend and ally, not your enemy. This will miraculously transform your whole life.”
― Eckhart Tolle