It's more unusual for children to write words and sentences backward. You may want to have your daughter's vision checked to make sure that she is seeing well. If her vision checks out okay, you may want to investigate the possibility of a learning difference.
Since it is the end of the school year, you could give her eyes a few more months to mature over the summer and monitor your daughter at the beginning of next year. During the summer, give her opportunities to practice handwriting with fun markers and pens. You could also put a layer of pudding on a cookie sheet and let your daughter practice writing with her finger. (You can also use sand or cornmeal, but pudding is more fun.) Write words and sentences in "dot letters" on paper and let her trace over them.
Talk with the school counselor about the process you will need to follow if you decide to have your daughter tested next year.