Sounds like a vocab issue rather than comprehension issue. We have that in our house, and it's especially clear to see when our newly 5yo (bilingual) reads in his weaker language, where he has of course a less rich vocabulary.
My instinct is to say let it be, since you will want her vocabulary higher if she's going to be reading even harder books in her head. Plus, it's almost the end of the year.
However, if your school is like mine, and they automatically place the children in a lower level at the beginning of the year (probably because it's a very results-driven school so the teachers need to show progress), I'd push for a higher level, since you'll also get additional development over the break. If you think the school will be sensible about levels when she starts next year, it's less of an issue.
