Thanks so much for these additional responses! I was out of town all last week, so I apologize for the delay in my response.

Polarbear, vision is definitely an issue that has not been on our radar. Thanks for alerting me to this idea. She has never had her eyes or vision checked, except the routine checkup at the pediatrician. One question - she is very good at drawing, as well as things like hidden pictures puzzles. Do you think this makes vision issues less likely?

Platypus, lots to think about in your response! As far as I can tell, the reading instruction at school has been based more on drilling sight word recognition and using picture clues than on phonics, although they certainly do incorporate some phonics. She may well be a kid who needs a more phonologically-based teaching method. Coincidentally, on my trip I was catching up on podcasts and happened to listen to this - right on topic:

https://www.apmreports.org/story/2017/09/11/hard-to-read

The headline focuses on students with dyslexia, but the article makes the point that Orton-Gillingham or other phonics-based methods are more successful for the general population of students as well.

Kai - it's very interesting to hear from someone who realized an older child's giftedness due to the younger child. I feel like I've almost exclusively heard of it happening the other way around, so our situation has just felt odd to me.

In terms of a general update/response: We do have some concerns outside of reading (mostly attention-related, also some issues with social anxiety, which we just started working on with some therapy). I think we are going to get her on the waitlist for a full neuropsych evaluation. The responses I've gotten here have been helpful in getting me over the hump to think there's enough of a chance of an issue to be worth pursuing. I believe the waitlist is about 6 months, so if we change our minds or find something else (e.g. vision issues) going on in the meantime, we can always cancel. In the meantime, we'll see where she is with reading at our parent-teacher conference next month. She just changed schools, so it's possible things will improve (same district, though, so likely not much change in instructional practices). If she's still struggling, we will likely try out the All About Reading program at home as well as consider asking the school to do a special ed evaluation.