Yes, this has been a problem. We did let her read alone for the last year and this is likely related. We now sit with her again when she reads out loud to us and we have her write down any words she does not know in a journal (which has helped). However, the problem still remains with her speed (and we keep saying slow down). I learned how to speed-read in high school and it was really helpful in college, but she speed reads by actually reading all the words out loud (reads a mile a minute).
I like that idea of the most important thing as that seems like a really good approach.