Is your child more cooperative with showing you what she knows?
I think perhaps because I've never pushed her to show me anything, she's never bothered to hide anything from me. She is reading to me right now (and the fact that I'm obviously ignoring her to write this post should be an indication of how often she does that).
The flip side is that of course there could be many things that she can do that I'd never know, because I don't really ask her to show me things.
There are a number of different skills that go into reading level, and fluency and interest are part of it. I think it's relatively common for kids to be able to decode much higher level words than the books that they can read fluently (or that they want to read fluently). DD can probably decode at a 6th grade level or beyond, but I wouldn't call that her reading level since she'd be bored to tears reading a 6th grade book from start to finish. I've seen her read 4th grade level books cold, so, as far as I'm concerned, that's her level.
Also I think it is pretty common for new readers to be reluctant to read in front of people who react to their reading. My DD basically refused to read in front of my parents the last time they visited after my silly dad made a fuss when she read a street sign.
Anyway, all that to say: give it some time. As you said, you really don't need to know, and by the time you've figured it out it's likely to change anyway.