It could simply be that she has been producing some insulin herself still - many have a 'honeymoon period' when first diagnosed, but this has stopped now. A bit more info would be helpful for people to answer though.
What time are her injections and breakfast? Does her reading stay high or start to drop back down again? Could she have a bit of a cold or anything like that? And I hate to ask this when we're talking about a 6yr old, but could she be stressing about anything at school the last few days?
Somebody on here will be able to give you some advice I'm sure x