There are some infections you can wait out, but a bladder infection isn't one of them. It can quickly and easily spread to their kidneys and cause irreparable kidney infections. Also, the worse the infection is and the longer it goes untreated the more likely it is that your child will have chronic bladder infections. It may seem that I am blowing things out of proportion, but my daughter has struggled with bladder infections since she was 3 years old; she is turning 9 next week and still has trouble.
Here are some notes we have learned on bladder infections over the years. Cranberry juice, even 100% cranberry juice, is not potent enough to treat a bladder infection. The sugar in it actually feeds the bacteria, and ALL cranberry juice has sugar; otherwise it is too tart to drink. You have to get cranberry extract supplements like Azo to do any good. Also, the cranberry extract is not a treatment for an active infection, but it can help prevent them. Once your daughter is free of her infection I would recommend having her take cranberry pills to help keep future infections at bay. Also, a high fiber, low sugar diet really helps. It keeps her insides from being more of a breeding ground for bacteria than absolutely necessary. Many bacteria that cause bladder infections are resistant to many antibiotics so after she is treated keep a close eye on her. She may have symptoms recur after a week or two. If she does, it's the same infection and you need to get a different antibiotic. This can happen over and over again like it did with our daughter. If it recurs more than once see a pediatric uroligist; pediatricians are just not good at treating stubborn bladder infections. If they persist they will do a VCUG and see if she has a physiological problem that is causing the infections. If she does they may recommend that you put her on an antibiotic long term. I would try to avoid a long term antibiotic unless absolutely necessary. There is new research that strongly indicates that long term antibiotic use, particularly for some of the antibiotics used for bladder infections, can cause Type I diabetes. My daughter is now a type I diabetic and I am sure that is what caused her diabetes. However, there weren't really any other options when she was 4. Now a child with chronic infections can have a procedure done called Deflux that is very simple, fast, and effective. Opt for that over long term antibiotics.
I know this is way more information than you wanted, but we have a long history of this and are just getting off of another set of infections so I have it on my mind now. Good luck! Also, I don't mean to scare you about the chronic stuff; your daughter will probably be fine. I just thought I would fill you in with some of the information we have learned over the years if it does end up being a problem.