Why does my 9year old dauggter have trace amounts of blood and protein in urine?

Multiple sources. Trace blood/protein can be a random false positive on the test or represent contribution of these substances from anywhere in the urinary tract.(kidney to outlet) at trace levels, significant kidney problem is unlikely. If the sample was just squirted & not done with labia spread it can include vaginal debris.It is worth repeating at some point with the above in mind.
Menses. They are mild anyway.Trace are neglible unless she had other signs and symptoms?Why did she have a urine test done in the first place? Is she vomiting or have diarrhea? If she has her menses, not to worry.You can have test repeated for peace of mind.