What Causes Lump In Lower Abdomen Of Child While Recovering From Flu?

I have a four year old granddaughter. She had strep throat/scarlet fever about a month ago and then what I believe to be the flu right after that. Then about a week ago we discovered a hard egg size lump on her lower left abdomen between her hip and pelvic area. We took her to emergency room and they did an utltrasound and said it may be a cyst and she had a UTI. We took her into doctor on Monday and doctor said she didn t have UTI and was not sure what the lump was but would set up a consultation with a group of surgeons. Said we should hear from the within 7 to 10 days. Well this is my granddaughters life!!! I am very anxious and so afraid of what could happen in this time if it is something serious. If anyone is familiar with anything like this please let me know.