Anyone have a late reader?

Hi everyone. I’ll try not to be too long-winded here, but I’m a bit stressed about this. My daughter is 8 1/2 and is still only able to really read material that is quite easy (ex. “Level 1 I Can Read” Books, such as the “Little Bear” series). I used How To Teach Your Child To Read In 100 Easy Lessons to teach her to read and now she is making her way through the Learning To Spell Through Copywork books by Queen homeschool to help reinforce phonics rules, etc., which I’m hoping will make reading a bit easier for her. She reads a little silently each day and then re-reads it to me aloud so I can check her progress and offer encouragement, but it seems so slow and just like it’s really “tiring” for her mentally (and sometimes, it seems, physically). She’s had her vision checked and does wear glasses for reading (not a very strong prescription). This is the first of my children that I have taught to read (our other daughter we removed from public school in grade 2 and she already knew how), so I’m very worried about her progress. Have I done something wrong? Is there anything I can do to help her along? I would appreciate any advice or suggestions! Thanks.

Rachel