C.W.
Hi VM...
Sorry to say, but in MY experience, cranberry juice can help 'keep' a UTI from coming one...(maybe)...but NOT cure one.
They are going to want a 'clean catch' urine specimen I suspect...IF you have a sterile cup...with a lid...you can try to 'catch' one right prior to doc appointment...BUT might be better to have them 'catch' one there...they have the cups...and one type for kiddos that has an adhesive around the cup to help with a sterile 'catch'...
But at six...maybe give fluids right prior to appointment (or on the way) and do NOT let her pee til she gets there...
Best Luck!
michele/cat