I used to work for Sylvan Learning Center, and deal a lot with the schools. Yes, you can request testing. Legally, the school has to follow up. The teachers are professionals, and if they say it's too early to test, then the testing they have does not accommodate a child of 7. You can press the point and get the testing, but in the end it may not be valid because of the age of your child.
My advice is to continue working with the child. Don't make a big deal out of the letter switching, or she will become defensive about it and worsen the issue. It is not uncommon for children younger than 3rd grade to confuse b/d or even p/q and 9/6. If she were writing whole words backwards, that would be more alarming. But it is still early. I agree on getting help the soon the better. I also agree with a previous post that advised focusing on auditory learning. Read to her A LOT! Back off from asking her to perform in reading. Children learn more than we know by listening to stories being read to them. They hear inflection in our voice and if they know enough to follow along while you read, they can learn how to pause correctly for punctuation.
If you are still concerned, you can take her to Children's Hospital for testing, they should have age appropriate testing, but dyslexia is difficult to diagnose because mixing up b/d is common for youngsters learning to read.
www.bookadventure.com is a great free service that allows the child to tell the site what kind of books they like and then take comprehension quizzes.
Good luck and keep reading!