This is OP - thanks everyone for the comments.
We did take our DD to a pediatric ophthamologist, who said that DD's visual acuity, binocularity and tracking were all fine. However, he could not explain to me why DD rubs her eyes and/or leans all the way down covering her left eye when she reads, has complained that print is blurry (she's also said that small font looks like it's moving), and she has trouble reading small print on things like a ruler. She also has much more trouble processing information that's presented visually vs. orally (e.g., she'll completely "not see' instructions or entire questions on tests, but she has no problem attending to verbally presented instructions). All he had to offer is that DD might benefit from academic tutoring. That didn't make sense to me, so I wanted another opinion.
The optometrist did a number of tests with DD to test how her eyes function as a team - the testing was much more detailed than what the ophthamologist did. DD can see things at a distance just fine, but her issues are with saccades and convergence. So, if you bring a pencil from a distance to DD's nose, she'll start to recoil in discomfort at about 6 in. away; she can read a vertical column of numbers with no problem, but she has difficulty reading horizontally across with accuracy (e.g., she'll skip words, lose her place, cover one eye, etc.). The optometrist did recommend vision therapy in addition to the glasses to target the weak areas. I didn't find the VT recommendation unreasonable (est. 6 months, once a week, plus at-home exercises). I realize others such as the PP (and DH frankly) are skeptical.
As I see it one of three things is happening: (1) DD doesn't have a vision issue, and any issues she has are neurological in nature. (This is the ophthamologist's view.) (2) DD has a vision issue, but there's nothing that can be done about it. (That's where we are now.) or (3) DD has a vision issue, and there is something that can be done about it. (Optometrist's view.)
The vision therapy exercises (for example, training the eyes to better track text across a page) make sense to me. It seems to me we've pinpointed the source of DD's issues, and I'm not aware of any way to address them other than what the optometrist recommends. Again, the ophthamologist provided no meaningful help. If anyone has any other ideas, I'm all ears!