Most bugs thrive in acid environment in the body.  So try to give her the foods that are alkaline forming from the gut down and which turn the pee to alkaline PH as this will make it more difficult for any bacteria to thrive.  It will also make it good for the good bacteria, as they keep the bad bacteria at bay.  

Food that turns blood, tissues and urine alkaline ironically are fruits and vegetables and water has a ph of 8 value of 8 so things like cranberries and water are not such a bad idea.  Blueberries also. Anti biotics are not really good because they kill off one bacteria, but then you may get an imbalance of other bacteria colonizing in the urinary tract due to the lack of the other, especially if the anti bitotic was not broad spectrum.  Been there and had this happen and it took months to be right.  Far better to increase the good bacteria with something like acidophilis yoghurt both down below and orally.  These are things I do when an infection flares anyway these days and it actually goes away.  To alkalinize the urine, try 1/2 tsp in a little water.  Adults take 1 tsp in cold water.  It will actually soothe the urinary tract and calm down inflammation. 

I know it is all anotomical based, but the more you can keep the urinary tract alkaline the better.  Things that make the pee more alklaine are dairy products like milk etc and cheese.   You can usally get away with live yogurt though.  To increase calcium, the best thing to do is increase green vegies like broccoli, mesculin and even try lettuce.  Some kids may not eat their greens, but because milk is high in protein it is quite alkaline and it therefore means less calcium can be deposited in the bone any way.  So consequently most of it ends up in the toilet.  Especially the type of milk that is very low fat.  The lower the fat the higher the protein value.  The best way to increase calcium is eating greens, keeping your body tissues, blood and urine alkaline and weight bearing exercise which most kids do anyway.  It is not made higher with increased dairy foods.  The only thing to gain from milk are baby cows.  LOL! 

Anyway off track here but another good thing is a little organic cider vinegar in a glass of water with a touch of other juice or something to flavor it.  It de-acidifies the urine and also helps to digest and balance any acid foods you eat in the diet such as meat protein, dairy and sugar.  Cut sugar in the diet as it is a nuisance and feeds bacteria.  I am presuming she just get’s these every now and again and in that case, it is far better to work at prevention than the cure they offer anti- biotics as they stuff with the immunity completely.  I would not really take anti-biotics unless it were something quite serious.  This sounds like it with blood in the urine and it can lead to kidney damage if not dealt with. 

Most of the above advice is for how to avoid this stuff for her  when she is well again though.  When she has got over the anti-bitotic treatment give her acidophilis during and after that for a few days to get the normal bacteria levels well again in the gut etc and then follow the above to avoid it happening again for her.  I guess trying these can only help.  Do a search on Google for Alkaline and Acid diets and it throws a lot up that you can study to help her avoid those episodes.

Regards,