yes there is a such thing as false positives and false negatives, which my little boy keeps getting after 3 test. But despite that, you have to look at the main symptoms. Enlarged lymph nodes/glands, fatigue, enlarged spleen. If thats the case then she has mono. This is the 2nd time my little boy has it! The first time was last year just before halloween. Still don't know how he got this. But they say his symptoms can come back at anytime. This time is way worse. He's actually in the hospital now. As far as the rash. Thats also a sure sign of mono. If a child is given medicine to treat strep or something similar that goes along with mono, and actually as mono also, they can and most likely will develope a rash. Just keep a close eye on her and make her rest! Don't let her be to rough for at least a month, because her spleen could burst. Hope everything works out for the both of us!