Hi, LM4G,
Lots of times it's 4th or 5th grade before these disabilities are diagnosed because that's when cognitively kids should have worked out these things. So that's when the benchmark is kind of set.
My son has dysgraphia. It is like dyslexias backward first cousin. He can take in the information but can not put it out in clear written form. It's a processing disorder. If you were to ask him the question he could give it to you verbally, but couldn't write it out. He can't spell worth a darn, his handwriting is on a second or thrid grade level (he's 18), and his written structure is disjointed, awkward and confusing. It has absolutely nothing to do with what he knows or is capable of learning, but what and how he can share what he knows.
Have you talked to her teacher? Does she see any need for concern? The only real way to diagnose is to test and I would start at the school. Set up a meeting with the teacher and school counselor and address your concerns to them. Find out if they see her struggle. If they do, then request testing for learning disabilities. If they don't and you are still concerned, you can get a referral from you PCP and have them done yourself.
If you are concerned then that's enough to push for difinitive answers, because if you are going to be wrong, let it be that she doesn't have a problem rather than she did and no one noticed.