I assume by 'pus pockets' that you mean that your daughter has pus covering the surface of the tonsils when you look in the back of the throat. This sort of throat infection can be cause by a number of different bacteria and viruses, including the strep and mono that she was already tested for. Unfortunately, since there are so many different potential infectious causes, it is often hard to tell what is exactly causing the infection, if the strep and the mono come back negative. Fortunately, in most cases, it does not matter, because with close attention and care from her pediatrician
, the condition generally tends to resolve without any serious complications.
If, on the other hand, by pus pockets you mean that your daughter actually has a deeper infection inside the throat, then this is potentially more serious, because it might require drainage of the pus or hospitalization and intravenous antibiotics to get over the infection. If this is what is going on, it is important to act quickly before the infection has a chance to spread or worsen.
Your pediatrician will be the one who is best able to guide you through this process and give you the advice you need. Please continue to discuss this issue with him or her!