Here are two tricks you can try. One is to write the word "bed" on a piece of paper and then draw a bed around the word. Point out the bed begins with /b/ sound and ends with a /d/ sound. If she knows how to spell bed, she should be set.
Another visual you can use is to form a capital B and point out that the lower case b can be found in the capital letter (the lower part of the capital).
If you are still noticing reversals, bring it to your daughter's teachers. There may be a learning problem that can be nipped in the bud at an early age. Believe, I know from first hand experience.